Urban traffic accidents: the case of Montijo
Mariana Fragoso de Rhodes Baião Abstract:
Portugal has shown a very positive evolution in reducing road traffic accident fatalities in the past decade. Hence, it is necessary to address the issue of road crashes in a smaller scale, in the municipal level, reducing the number of severe and light injuries as well. Thus, this study analyses the patterns of road traffic accidents in a Portuguese municipality: Montijo.
A literature review of the state-of-the-art approaches in black spot analysis was performed and in correspondent counteractive measures as well. The road crash data collected for Montijo was analysed and a black spot detection methodology was applied, based on the currently used severity indicator and on a suggested indicator, calculated through accident costs. As a result, 11 black spots were identified. Several counteractive measures were proposed, within the traffic calming methodology, aiming to prevent the occurrence of severe and light injuries by reducing traffic speed and control traffic flows.
Keywords: Black spots, road traffic accidents, severity indicator, traffic calming, urban traffic accidents.
1. INTRODUCTION The roadway environment is formed by the interaction between three factors: the road, the vehicle and the human element (Macedo, 1999). This paper aims to study the first factor, the road, in order to detect fragilities and propose possible solutions, within Road Safety Engineering. An accident occurs when a driver is unable to meet the challenges presented by the roadway system (Geurts and Wets, 2003). In fact, the link between the driver and the road is the most crucial part of the road environment, and were it is most urgent to take action in reducing risks. It is necessary to improve the safety of the infrastructure, in the phase of design as well as maintenance, and the response of the driver/pedestrian to adjust his behaviour to the risks that may appear in his itinerary. In order to improve road safety in European countries, there has been a huge investment in the implementation of safety measures and in the achievement of lower values of road traffic accidents indicators, such as the number of road fatalities per million inhabitants. To achieve these goals, countries have developed national strategies for road safety in order to define the areas in which it is most urgent to act and set internal targets so each territorial unit could play its part in the pursuit of the general goal. Currently, in Portugal, the road safety strategy is focusing on the municipalities once there have been developed guidelines for the elaboration of municipal road safety plans. Therefore, this paper aims to study road safety in a Portuguese case study municipality (Montijo) analysing several indicators in order to identify road traffic accidents black spots, and suggest road safety measures to correct them. The proposed safety measures are traffic calming measures, aiming to reduce road accident indicators by controlling traffic volume and speed. The choice of the case study of Montijo was based on its geographical characteristics, which include urban and rural areas, as well as on the impacts this municipality is most likely to suffer with the projected future investment in High Speed Railway, and the new Lisbon airport, due to the proximity of the location of these transport infrastructures to this municipality.
1 2. ROAD SAFETY 2.1 Road Traffic Accidents 2.1.2 Road traffic accidents in Portugal and in the EU In Portugal, the number of deaths in road crashes per million inhabitants has been decreasing since 1996 (Figure 1), bringing this country closer to the European average values for this index. Portugal has come a long way in the pursuit of the goal established by the European Union (EU) that consists of reducing the number of fatal victims in road accidents by 50% by the year 2010. However, one of the aims of this country’s National Road Safety Plan (PNPR) in 2003, to place this country above the European average, is proving to be difficult to achieve, as most of the other European countries are also showing an excellent performance in reducing their road fatality indexes, causing for the average values to raise higher and harder to surpass.
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1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Média Europeia 162 151 138 134 132 124 126 123 120 117 112 110 103 95 91 86 Portugal 323 310 271 251 271 272 250 210 200 184 163 160 148 124 119 91
Figure 1 – Road fatalities per million inhabitants in Portugal and the European average [ANSR, 2009 (edited)] In the beginning of the year 2010, a new concept of road fatality was introduced in Portugal, in order to match the standard definition applied in Europe. Until this date, the number of road fatalities was obtained by multiplying the number of deaths occurring directly from the road crash by a coefficient of 1,4, so it could be compared to the European road fatalities values, which accounted for the deaths deriving from the road accident up to 30 days after it took place. Nowadays, this same concept is being used in Portugal, but up to date there are yet to be known the results of this first year of its appliance. It is most likely that the number of road fatalities obtained with this new concept will be higher than the one calculated from the previous method, which might jeopardize this country’s positive position in the European context, bringing it further from its goals.
2.1.3 Road traffic accident analysis in Portugal In Portugal, alongside the reduction of the number of fatalities (Figure 2), there has also been an improvement in terms of crash severity, since 2008, substantiated in a reduction of the severity index applied by the National Association of Road Safety (ANSR) of 40%. This index accounts for the number of fatalities per 100 accidents which resulted in personal injury (light injury, severe injury or fatal injury). Also the number of light and severe injuries has decreased around 30% until 2008 (Figure 3). At the present time these types of injury are not used to
2 characterize and compare road safety in Europe, but with the positive results in reducing traffic deaths that have been verified all over most European countries in the past years, the need to establish objective goals, within the EU, that include reducing every type of injury in road crashes is arising. Of all the road safety measures that have been implemented in Portugal since 1988, the ones which have shown the best results in road safety indicators were the National Road Safety Plan (PNPR) in 2003 and the updating of the road legislation enacted in 2005.
2000 10000 1748 7597 1500 8000 6000 1000 874 3799 4000 776 500 2000 2606
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Fatal injuries Goal set in the PNPR in 2003 Severe injuries Goal set in the PNPR in 2003
Figure 2 – Road fatalities between 1998 and 2008 and the Figure 3 - Road severe injuries between 1998 and 2008 and goals set for 2009 [ANSR, 2008 (edited)] the goals set for 2009 [ANSR, 2008 (edited)] One of the aims of the PNPR was to reduce the number of road fatalities and severe injuries by 50% until 2010. According to figures 2 and 3, both these goals were already achieved by the year 2006 and these indicators kept improving until 2008. In fact, by 2008, all the goals set on the PNPR for the reduction of fatal, severe and light injuries for 2010, were already achieved. Only the number of traffic deaths in urban agglomerations hasn’t had such a favourable development as of yet, but is likely to achieve its predicted goal by 2010. It is also based on this result that this paper aims to study road traffic accidents in an urban agglomeration, the municipality of Montijo. The analysis of the evolution of road traffic accidents in Portugal from 2006 to 2008 performed in this paper was based on severity indexes, which intend to demonstrate the human consequences resultant from the crashes. The applied severity index was set by the National Association of Road Safety (ANSR) and represents the number of road traffic fatalities in one hundred injury accidents. a) Evolution of road traffic accidents throughout the year in Portugal
2006 2007 2008
4,0 3,0 2,9 3,0 2,4 2,6 2,5 2,4 2,0 2,1 2,1 2,1 2,1 2,0 1,6 1,0 0,0 Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec
Figure 4 – Monthly evolution of the severity index [ANSR, 2007 and 2008 (edited)]
3 The months which showed higher road crash severity were March, April, August and November, whereas May, June and October were the ones with less severe accidents (Figure 4). Both in June and in August, there was an increase of the severity of the crashes from 2006 to 2008. February and July, however, showed a decrease in this index. The other months did not show a clear rising or descending tendency in the three years in study. b) Evolution of road traffic accidents throughout the week in Portugal
2006 2007 2008
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Figure 5 – Weekly evolution of the severity index [ANSR, 2007 and 2008 (edited)] According to figure 5, the accidents with more serious consequences tend to happen on the weekend, especially on Sunday. On the other hand, the day of the week with less severe accidents was Wednesday. Throughout the week there was a growing tendency in the severity of the crashes, from its lower value, on Wednesday, and its higher value, on Sunday. The days of the week with two of the highest severity indexes in 2008, Sunday and Tuesday, also happened to be the ones that demonstrate a growing tendency from 2006 to 2008, which is a situation to monitor in the future. Thursday and Friday, both showed a decreasing tendency from 2006 to 2008, to the second lowest value of crash severity. c) Evolution of road traffic accidents throughout the day in Portugal
2006 2007 2008 7 5,7 6
5 4,2 4 3,3 3 2,3 2,1 2 1,7 1,7 2 1 0 00h-03h 03h-06h 06h-09h 09h-12h 12h-15h 15h-18h 18h-21h 21h-24h Figure 6 – Hourly distribution of the severity index [ANSR, 2007 (edited)] The periods which showed higher road accident severity were between midnight and 6 a.m. (see figure 6) which represent about twice the values observed in the other periods of the day. Moreover, it was in this period that the least number of accidents occurred, so this is most probably related to the higher consumption of alcohol from drivers. The least severe accidents took place from 9 a.m. to 3 p.m., which is a positive result, as it includes the period of the morning rush hour, were traffic volume is intensified. The chart showed a growing tendency of accident severity from its lowest value, at 9 a.m., to its higher value, at 6 a.m.
4 d) Evolution of road traffic accidents per road type in Portugal
2006 2007 2008
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Figure 7 – Distribution of the severity index per road type [ANSR, 2007 and 2008 (edited)] The classification of roads in Portugal is divided as follows, according to its traffic volumes and number of lanes: Motorways (AE), National Roads (EN), Main Roads (IP/IC), Municipal Roads (EM) and Urban Streets (Arr). According to figure 7, the type of road with the highest number of severe accidents was the IP/IC, which was also the type of road were a lower number of accidents occurred. This is most likely related to the inadequacy between the speeds practiced there and the characteristics of the infrastructure. On the other hand, the streets were the type of road with lowest accident severity and at the same time the one were the highest number of accidents occurred. As this severity index takes into account only the number of fatalities, this may indicate that the types of injury more common in the streets are severe or light injuries. Moreover, as lower speeds are practiced in this type of road, it is more likely that the consequences are less severe. The case study in this paper aims particularly at this type of road, in a municipal scale, in order to focus on the reduction of the number of severe and light injuries, which are not the main issue on a national scale.
2.1.4 Rural and urban traffic crashes
Figure 8 – Road crashes per location in 2008 (ANSR, 2008) Urban and rural areas show distinct characteristics not only in terms of occupation, but in road networks and circulation patterns as well, which reflect inevitably in their road safety performance. Rural traffic is lighter than urban traffic, with longer distances to travel and therefore higher circulating speeds. Lower traffic flow means less chances of vehicle collision, which results in a lower number of accidents amplified by the fact that fewer accidents are reported in rural areas (Cardoso e Castilho, 1985). Nonetheless, as circulating speeds are superior,
5 the consequences of the accidents are more severe, with a higher percentage of road fatalities than severe injuries (figure 8). On the other hand, a higher number of road crashes occur in urban areas, but resulting in less severe consequences, with a percentage of road fatalities inferior to that of severe injuries (Macedo, 1999). Also a higher number of pedestrian accidents occur in urban areas, but mostly because pedestrian traffic is not as common in rural areas as in urban areas. Other than high circulating speeds, also higher alcohol consumption, lower use of seatbelts, less maintained infrastructure and higher travelling distances to medical care facilities are identified as most common causes for severe accidents in rural areas.
2.2 Severity indexes and indicators Road traffic accidents analysis are very often based on severity indicators and indexes, which enable a clear view of road crash patterns and an understanding of the variables which influence those patterns. In order to study a severity indicator which took into account all three types of injuries (fatal, severe and light injuries) it was necessary to come up with a weight assigned to each type of victim, which reflected their relative severity. The calculation of these coefficients was based on the costs of accidents resulting in each type of injury, for which several documents regarding accident cost estimation in European countries were analysed. The analysis based on accident costs is particularly pertinent, when it is known that according to (Masniak, 2008), the countries that assign lower economic values to the prevention of a road fatality, Portugal being one of them, also happen to be the ones with worse road safety performances. Therefore, it is especially relevant that the calculated weights are fairly adjusted to the road safety scenario of each country and reflect accurately the importance assigned to the prevention of each type of injury. Many authors have studied the matter of estimating accident costs, but no conclusions have been achieved on which variables to consider in its calculation or even on the most adequate method to estimate human damage resulting from the crashes. The most complete method is the comprehensive costs method (Judicki, 1994), which comprises traffic accidents’ direct costs, property damage costs, medical and emergency systems expenses, legal and bureaucratic expenses, traffic delay, human productivity losses, and costs of pain a lost quality of life. In order to quantify these costs, the most commonly used methodology is the willingness-to-pay approach, that represents the monetary value that each person assigns to the desire to live further or improve its’ quality of life. The document which presents the most adequate cost estimation for this analysis was a report from the HEATCO project - Developing Harmonised European Approaches for Transport Costing and Project Assessment presented by the European Road Safety Observatory, which provides cost recommendations for each type of victim, and appropriate for each country’s circumstances (HEATCO, 2005). Table 1 indicates the costs mentioned in this report and the calculated weights for each type of victim. The weights currently considered in the severity indicator applied in Portugal (IGANSR), are also identified in table 1.
6 Table 1 - Costs and weights for each type of injury
Accident cost analysis IGANSR HEATCO Costs (€) Weight Weight Fatal injuries (M) 830.000 112,162 100 Severe injuries (FG) 107.400 14,514 10 Light injuries (FL) 7.400 1,000 3 From the calculated weights, the following indicator was obtained:
For the case study municipality, three indicators were applied and compared. Two correspond to the indicators obtained from the weights presented in table 1: IGCA e IGANSR. And the third one is calculated directly from the number of crashes resulting in any type of injury (IGAV). So, for the year i, the three indicators under study are as follows:
To enable the agglomeration of data from several years, the guidelines for the elaboration of Municipal Road Safety Plans suggest a road safety index (ISRM) that through a weighing system gives more relevance to the most recent years and less to the previous years:
In which i stands for the most recent year comprised in the analysis, and the indicators IGi, IGi-1 and IGi-2, represent the calculated severity indicators for the three years included in this study. This index can be calculated for the three indicators under comparison. However, the comprehension of this indicator is not very clear, as it would be expected that the sum of the considered weights should equal to the divisor (1,99≠3). Consequently, another index was developed, considering the same weights as the former, but changing the divisor, taking into account the two previous year as if they were only one: Both indexes were applied to the road traffic accident analysis elaborated for the streets of Montijo, in order to determine which should be considered black spots.
2.3 Black spot analysis In the identification of sites with a high concentration of traffic accidents, there are 5 basic topics to take into account: identification criteria, length, ranking, proposed safety measures and analysis of the results of their implementation. Having analysed several methods applied in other countries (Elvik, 2007), it was observed that some were relatively simple and others extremely complex. However, there is no common agreement on which are the most accurate in identifying black spots, although mostly predictive methods have been developed recently, looking to obtain the expected number of crashes calculated through accident prediction models. Nevertheless, the accuracy of these estimations depends heavily on the model’s adjustment to reality and on the quality and quantity of data available. Hence, the method applied in this document is a reactive method (PIARC, 2003), through the analysis of the referred severity indexes, based directly on reported traffic accidents.
7 Regarding black spot delimitation, many countries apply a sliding window with a fixed length, and every site with that length which surpasses certain thresholds is considered a black spot (Elvik, 2007). In this study, the length of the black spots was considered to be the length of the whole street, as that was the most detailed information about the location of the accidents that was obtained. Black spot ranking is especially relevant when it comes to setting priorities in road safety strategies, as most of the times there are tight budgets for black spot correction (Cardoso e Castilho, 1985). In order to obtain the best outcomes possible from the investments in black spot correction, they are more commonly ranked according to their improvement potential, that is, the probability of reducing a higher number of accidents with the implementation of a certain safety measure. In the analysis performed for the municipality of Montijo, all the streets identified as black spots were suggested for treatment, as no budget limitation was considered and no cost-benefit analysis was performed on the proposed measures. However, if there should be a fixed budget for their implementation, the proposed traffic calming measures are mostly inexpensive and very effective in reducing crash frequencies, and would most certainly have good results in any cost-benefit analysis that was to be performed on the correction of these black spots.
2.4 Traffic calming in urban roads The road safety measures studied in this paper are traffic calming measures, which aim at reducing traffic speed or controlling traffic volume. Since there are no records of data on traffic volumes in the case study of Montijo, this study focuses mainly on the traffic calming measures which reduce traffic speed. From all the measures being applied nowadays in many countries, the following have been considered the most effective: speed lumps, speed tables, raised intersections, roundabouts and traffic circles, chicanes and narrowings/chokers (BHTRANS, 1999 and Seco et al.,2008).
3. ROAD TRAFFIC ACCIDENTS ANALYSIS IN MONTIJO 3.1 Description of the municipality of Montijo
Figure 9 - Municipality of Montijo in Lisbon Metropolitan Area (Câmara Municipal de Montijo. 2008) Montijo is a very particular case between Portuguese municipalities, as it is formed by two physically separated territories (figure 9), East Montijo and West Montijo, with really distinct demographic and infrastructural characteristics. This paper focuses mainly on West Montijo which is the urban part of the municipality, occupying around 16% of the total municipality area, but holding around 86% of its total population. Also, the road network is much more organized in this area of the municipality, comprised by radial and diametric collector-distributor roads which allow for the proper dissemination of the traffic flow into and out of the urban centre.
8 3.2 Traffic accidents in Montijo 3.2.1 Data collection One of the challenges that presented itself in the development of this paper was in the collection of traffic accidents data for the municipality of Montijo. There is no standard registry sheet that can be filled in by authorities when reporting the accident that can provide the essential data to comprise a coherent and complete data base of traffic accidents. Unfortunately, the data collected for this analysis only includes 3 years, non- consecutive, two of them (2005 and 2008) lacking data for some months, and the data on other year (2008), only accounted for the accidents which resulted in personal injuries. Even so, the collected data resulted in an interesting analysis and led to some interesting conclusions on road traffic accidents in urban agglomerations. 3.2.2 Road traffic accidents analysis in Montijo
2005 2005 2007
2007
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Figure 10 – Monthly distribution of road crashes in Montijo, in 2005 and Figure 11 - Weekly distribution of road crashes in 2007. Data: CM Montijo. 2005 and 2007. Data: CM Montijo. From 2005 to 2007, the total number of road crashes in Montijo decreased by 30%, from 1009 to 729 accidents, which demonstrates that this municipality is close to achieving the goals set in the PNPR. Generally, road accidents tend to occur more often in the months of January, February and May (figure 10), but the existent data is not enough to derive any conclusions on seasonal behaviour of the accidents. Throughout the week, accidents are evenly distributed, having registered higher values on weekdays than on weekends (figure 11).
100 90 80 2005 70 2007 60 50 40 30 20 10
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Figure 12 – Hourly distribution of road crashes in 2005 and 2007. Data: CM Montijo During the day, there is a higher incidence of traffic accidents in the morning and in the afternoon rush hours, between 8 and 10 a.m. and 5 and 7 p.m. (see figure 12). Around 81% of the accidents that occurred in Montijo,
9 as well as in the entire country, are collisions; 17% are run-off-road collisions and only 2% are pedestrian crashes (figure 13).
Speeding (34%)
1% Reversing (8%) 45 1% 0% 292 Collisions Priority (13%) 0% 13% 32% Reckless driving (32%) Run-off-road 32% Road conditions (1%) 1401 collisions 13% Parking (1%) Pedestrian 8% Drivers' physycal condition (13%) Total: 1734 accidents Sudden pedestrian crossing (1%) Sudden animal crossing (0%) Figure 13 – Relative distribution of accident Figure 14 – Accident causes in 2005 and 2007. Data: CM Montijo types in 2005 and 2007. Data: CM Montijo Speeding and reckless driving are the cause of 64% of the traffic accidents in this municipality (Figure 14). Most of the accidents occurred in straight sections of the streets (68%), and only 12% happened in curbs (Figure 15). However, around 20% of the accidents took place in intersections or roundabouts (Figure 15). The fact that most accidents happened in straight sections, may indicate that traffic accidents are not directly related to road design, but to the driver’s capacity of identifying the risk and reducing its speed to circulate safely.
0% 0% 0% 0% 2% 0% 0% Straight section (68%) Good Weather 6% Curb (11%) 5% 11% 8% Roundabout (6%) Rainy Weather Junction (9%) 11% Intersection (7%) Parking (2%) Wet Weather 68% Speed Lump (0%) 89% Square (0%) Foggy Weather Gas Station(0%) Unknown (0%)
Figure 16 – Accidents per weather condition in Figure 15 – Accidents by section of road in which they occurred in 2005 and 2007 2005 and 2007. Data: CM Montijo
Only 11% of the traffic crashes occurred in bad weather conditions, as rain or fog (Figure 16). As the other 99% of the accidents occurred in good weather conditions, it can be concluded that the climate did not affect road traffic accidents in Montijo, in the years included in this analysis. Most collisions and run-off-road collisions were caused by dangerous manoeuvres and excessive speed. However, when it comes to the main cause of the accidents involving pedestrians, no conclusion can be drawn, as they fall in the “other” category, which provides no information on the matter. Some of the identified causes of pedestrian crashes are sudden pedestrian crossings, driver’s poor response, excessive speed and priority disregard. A similar analysis was performed for the accidents which resulted in injuries. In terms of personal injury accidents, they tended to occur on the month of October, in the three years included in this analysis. The distribution throughout the week of this kind of accidents did not show any visible trend, so no conclusions could be drawn on its evolution in the years in analysis. The hourly distribution of injury crashes, however, showed a clear incidence in the afternoon rush hours, especially between 5 and 7 p.m. In 2005 and 2007 they also were concentrated in the morning rush hour, but in 2008, their occurrence spread evenly through the whole morning period.
10 Most personal injury accidents in Montijo resulted in light injuries (88%), around 9% resulted in severe injuries, and the remaining 3% were fatal injuries. This distribution was similar in all three years included in this analysis. However, in absolute terms, 2007 was the year in which the consequences deriving from the accidents were more severe, showing a slight tendency to decrease in 2008. From 2005 to 2008, the total number of injuries resulting from collisions has been increasing, which leads to the conclusion that collisions in Montijo are becoming more severe over the years. On the other hand, run-off-road collisions did not result in any road fatality, and even though the number of severe injuries from this type of accident has increased, it can still be considered the less severe. Alongside, the consequences of pedestrian crashes have demonstrated an improvement, reducing the number of fatalities to zero in 2008, and the number of severe injuries to a third of the number recorded in 2005.
4. BLACK SPOTS IN MONTIJO 4.1 Identification and analysis In order to identify the traffic accident black spots in the municipality of Montijo, three indicators were calculated for each street in which there had been accidents in the years in analysis (IGAV, IGANSR and IGCA) and for each indicator, two road safety indexes (ISRM and ISRMprop) were determined and compared. When identifying the black spots through road safety indexes, a limit value has to be imposed, so that every street which results in a superior value can be marked as a black spot. In a municipal scale, the limit values have to be inferior, as crash severity is inferior than if we were working on a national scale. In this particular case, no fatalities occurred in the streets of Montijo, so lower limit values would have to be considered, for a reasonable number of streets to be identified through this analysis.
A limit value of 3 was applied on the ISRM calculated for the IGANSR, which meant that more than a light injury had to occur in every year included in this study, for the street to come out as a black spot. A correspondent limit value of 5 was tested on the ISRMprop calculated for the IGANSR. An amount of eleven streets were identified with this methodology (table 2). The limit values considered for the indexes calculated for the IGCA also intended to identify the streets in which there was at least a light injury in every studied year. On the other hand, the limit values considered for the indexes calculated based on the IGAV were meant to identify the street in which there had been at least one injury of any type in the three analysed years, as this indicator does not differentiate injury types. All the limits considered reflect a poor road safety performance in all three years, so that the analysis is not biased by a solo accident occurrence. In Table 2 the cells painted in grey were the streets which had values for each index superior to the considered limit values. Both IGANSR and IGCA identified the same number of streets. This indicates that the indicators applied currently are consistent with the monetary value assigned to each type of injury. As stated before, the
IGAV does not differentiate injury types, and ends up not identifying as many black spots as the other indicators. This may result in the exclusion of cases in which more severe accidents have occurred that would otherwise be identified and have to be treated as black spots. A good example of this situation is Av.ª Luís de Camões, which had two severe injuries and two light injuries (4 injuries total) and does not come out as a black spot in the IGAV.
11 Table 2 - Black spot identification
IG IG IG AV ANSR CA
Black spot ISRM ISRMprop ISRM ISRMprop ISRM ISRMprop
1. Av.ª de Olivença 1,55 2,32 7,07 10,61 2,89 5,38 2. Rua dos Combatentes da Grande Guerra 1,11 1,66 5,98 8,97 2,10 2,99 3. Av.ª Luís de Camões 0,77 1,16 5,42 8,14 6,69 10,15 4. Rua Joaquim Serra 1,22 1,83 3,66 5,49 1,38 1,83 5. Rua da Bela Vista 0,33 0,50 3,33 5,00 5,61 7,26 6. Av.ª 25 de Abril 1,55 2,33 5,32 7,98 1,88 2,66 7. Rua José Joaquim Marques 1,55 2,32 6,07 9,11 2,40 4,88 8. Av.ª dos Pescadores 1,33 1,99 5,41 8,12 2,07 4,55 9. Av.ª Fialho Gouveia 0,44 0,67 3,53 5,30 3,63 5,45 10. Av.ª Pedro Nunes 2,22 3,33 11,99 17,99 8,93 11,59 11. Circular Externa 0,99 1,49 4,30 6,45 1,49 2,15 ≥1 ≥2 ≥3 ≥5 ≥1 ≥2
The biggest differences between the calculated indexes for some streets are due to the fact that the ISRMprop assigns more relevance to the data from more recent years. In Av.ª de Olivença, Rua José Joaquim Marques and in Av.ª dos Pescadores the same number of severe injuries (1) and of light injuries (8) occurred. However, their indexes show diverse values due to the importance given to the injuries which took place more recently.
The streets with worse road safety indexes were Av.ª Pedro Nunes (radial) and Av.ª de Olivença (two sections: one circular and one radial). In both streets there was one severe injury and 8 or 9 light injuries.
The IGCA assigns higher relevance to severe injuries than the other indicators. The Av.ª Luís de Camões is an example of this statement, as it results in the second street with higher value for this indicator. In the IGANSR, this street does not stand out from the rest. It is thought that the importance assigned by the suggested indicator is more appropriate, as the elimination of the occurrence of severe injuries should be a priority in a municipal level.
A road traffic accident analysis was performed on the data collected for each street, and some general conclusions were drawn. All 11 streets have high traffic volumes, as they represent important accesses to the urban centre of the municipality, some being circular roads and other radial, allowing access to the urban centre. They showed similar traffic accident behaviour, characterized by a high occurrence of collisions caused by speeding. Furthermore, most accidents took place in straight road sections or intersections and in favourable weather conditions. Therefore, it is considered that the identified black spots would benefit from the implementation of traffic calming methods, as they aim to reduce traffic speeds and control traffic volume, which are both high in these streets, and also reduce the number of dangerous intersections, were many accidents took place.
12 4.2 Proposed road safety measures
Table 3 enumerates the streets identified as black spots, with the indication of the suggested traffic calming measures for each one of them and the correspondent schematic drawing.
Table 3 – Identified black spots and the correspondent counteractive measures
Black spot Proposed Safety Measure
Tighten curb radii 1. Av.ª de Olivença Centre island narrowing Raised intersections 2. Rua dos Combatentes da Grande Guerra Choker Raised crosswalks 3. Av.ª Luís de Camões Landscaping centre islands Placement of traffic lights 4. Rua Joaquim Serra Centre island narrowing Narrowing with on-street 5. Rua da Bela Vista parking Narrowing with on-street parking 6. Av.ª 25 de Abril Raised intersections Roundabout Narrowing with on-street 7. Rua José Joaquim Marques parking Raised intersections Roundabout 8. Av.ª dos Pescadores Raised crosswalks 9. Av.ª Fialho Gouveia Centre island narrowings Raised crosswalks 10. Av.ª Pedro Nunes Raised intersections 11. Circular Externa Centre island narrowings Neither speed lumps nor chicanes were suggested, because their effectiveness is questionable. Most speed lumps are detachable and therefore need to undergo frequent maintenance, and commonly, drivers swerve from their lane to avoid the lump, increasing the risk of collision with another vehicle. Chicanes are not easily accepted by drivers, because they interfere severely with traffic, and if they are not properly designed, they may cause for drivers to pass through the chicane in a straight line, also increasing the risk of collision with another vehicle.
5. CONCLUSION Although road safety indicators seem to show a tendency to reduce the number of fatal victims and injuries in road crashes, these results are by no means satisfactory as these numbers stand for damaged human lives and consequent loss of productivity, with heavy impacts on social and economic levels. The participation of municipalities in the pursuit of goals set for road safety is crucial to achieve a positive performance in reducing road accidents indicators on a national scale. With the commitment of the municipalities on achieving better road safety levels, there is much to profit from comparing results and trading experiences between them, so the standardization of accident reports and collected data is essential. The dissemination of a single report sheet to be filled in by local authorities at the time of the crash would be very useful to build a complete nation-wide data base of traffic accidents attached to a network with accident geo- positioning to obviate the detection of patterns in road crash occurrence and their characteristics.
13 Black spot identification thresholds have to be set at a municipal level, so each local government can sort out its own road safety strategy, and allocate the necessary budgets. Severity indicators should consider accident costs, and be fixed at a national level, so they can reflect the population’s monetary valuation of the prevention of personal injuries. The thresholds applied to the identification of black spots should be set internally by each local government, taking into account the patterns of road crashes and the specific characteristics of road traffic and the road network of each municipality. Traffic calming measures have proven to be the most effective in reducing traffic accidents with a small implementation cost. Therefore, it is suggested that a cost-benefit analysis be performed in order to study the most profitable measures in each black spot, so they will be more commonly applied in a municipal approach of road safety.
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