Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Addressing Expressway Traffic Management Issues in the

Ricardo G. SIGUA Hilario Sean O. PALMIANO Professor Assistant Professor Institute of Civil Engineering, Institute of Civil Engineering, College of Engineering College of Engineering University of the Philippines University of the Philippines Diliman, City, Philippines Diliman, , Philippines Tel/Fax: +63-2-9294403 Tel/Fax: +63-2-9294403 E-mail: [email protected] E-mail: [email protected]

Abstract: This study tackles several expressway traffic flow and driver behavior issues observed in Philippine expressway. Expressway management concepts, namely, speed regulation, vehicle spacing, and lane management are outlined and discussed. Speed and headway analysis are performed. Appropriate speed limits and schemes to achieve lane management and checking vehicle spacing to enhance expressway flow safety are recommended.

Key Words: expressway traffic management, speed limit, lane management

1. BACKGROUND AND OBJECTIVE

The operation of expressways in the Philippines started in the 1970s. The North Expressway and the , the first 2 expressways connect Metro to the northern part and the southern part of Luzon, respectively, providing faster travel to and from the suburbs and the provinces. Around 265km of expressways have been planned in the early 2000 covering both urban (within ) and outer areas (ALMEC, 2000). Currently, the expressways in operation are shown in Table 1.

Table 1. Expressways in operation in the Philippines (Inquirer, 2010) Start of Expressway Length, km. No. of lanes operation Daily volume

NLEX 84 4-8 1970s 158,000

SLEX 48 6-8 1970s 160,000

SCTEX 94 4 2008 30,000

9.7 (elevated) 4 1999 30,000 Metro Manila 13.4 (at-grade) 8 70s 150,000

Star Tollway 42 4 2001 30,000

Manila- Coastal (not 6.6 4 2006 Road available)

(not Subic-Tipo 8.5 4 1996 available)

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Almost all data used in this study are for the (NLEX), an 84- kilometer tollway connecting Metro Manila with provinces to its north, specifically those in the region. Much has changed in the operation of the facility since its reopening in February 2005 following rehabilitation work. The number of lanes has been increased to improve its capacity; modernized toll plazas with more tollbooths were constructed thus providing better operation; ETC system was also introduced during its reopening; and pavement condition has been greatly improved thereby providing better riding comfort. Associated with these improvements are a number of issues related to traffic safety, which need to be addressed and corrected. These include speeding, frequent lane changing or swerving, tailgating, and others. The paper focuses on addressing these issues and give recommendations to improve safety.

The specific objectives of this study are (1) to investigate speed and other traffic management issues in Philippine expressways using data obtained for the North Luzon Expressway (NLEX) and (2) recommend appropriate expressway flow management measures to improve safety based on analysis of speeds, headways, and accident information.

2. TRAFFIC MANAGEMENT ISSUES

2.1 Road crashes

In the North Luzon Expressway (NLEX), 1,653 road crashes were recorded in 2006. The frequency of road crashes increases near or within the vicinity of the toll plazas and interchanges. More than 45% of the crashes occurred near or within the vicinity of the toll plaza and interchanges. Most of these road crashes were attributed to miscalculations which happened due to sudden change/reduction in speeds.

Sta. Rita Interchange

Balintawak San Sim

250 Pullilan Interchange Toll Plaza Interchange Interchange Fernando Sn

200 on Interchange Dau Toll Plaza Interchange

150

100

# of # Accident 50

0 8000-8099 11300-11399 13000-13099 15400-15499 17200-17299 19400-19499 21600-21699 24400-24499 27100-27199 30500-30599 33100-33199 36000-36099 38800-38899 41100-41199 44700-44799 48000-48099 50400-50499 52900-52999 54900-54999 57400-57499 60400-60499 64500-64599 67700-67799 70300-70399 74500-74599 77900-77999 81500-81599 87400-87499 Location Manila

Figure 1. Road crashes along NLEX (Source of Data: TMC, 2006)

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

2.2 Speeding

Data on speeds of vehicles per lane and averaged every hour in the year 2006 at key locations along NLEX was used to estimate the percentage of vehicles running faster than the posted speed limit of 100 km/hr (or 80 km/hr for segments nearing Metro Manila). The speed values presented here therefore are conservative since the source data are not actual spot speed distributions but are averaged hourly data. Nevertheless, it clearly can be seen from Figures 2 and 3 below that a good number of vehicles traveling along NLEX are violating speed limit regulation.

Figure 2-a. Speed-Volume Plot (Balintawak, Northbound, 80kph speed limit)

Figure 2-b. Speed-Volume Plot (Balintawak, Southbound, 80kph speed limit)

Propensity for speeding along the expressway could be validated from the motorists’ apprehension profile along NLEX. Data reveals that next to overloading which accounts to about 24% of the total violations, speeding violation ranks second with about 18% of the total violations (TMC, 2006).

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Figure 3a. Speed-Volume Plot, Bocaue Northbound, 100kph speed limit)

Figure 3b. Speed-Volume Plot (Bocaue, Southbound, 100kph speed limit)

In the earlier discussion on road crashes (Figure 1), it could be noted that the greater percentage of crashes (about 55%) occur along expressway basic sections where significant number of vehicles tend to operate over the speed limit. Whether high traffic speed translates to more road crashes is unclear and remains to be proven. In fact, the safest highways in the world are the expressways and freeways, where very fast speeds are observed. However, there is a very strong indication that road crash severity is very much related to the speeds of colliding vehicles

The term ‘speeding’ is a relative word and it is defined based on legal maximum speed limit imposed on a given . If the maximum speed limit is arbitrarily set too low, then naturally, a large percentage of vehicles would tend to drive at a speed higher than the imposed limit. The issue that emerges here therefore is how to set the appropriate speed limit in the local expressways.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

2.3. Tailgating and sideswiping

Table 2 gives the top 3 causes of road crashes along NLEX in 2006. Rear-end collision is the most common. This road crash type is caused primarily by tailgating or following closely. The data also shows that next to rear-end collision, sideswiping is another major type of road crash accounting about 19%. This road crash type is normally attributed to miscalculated lane changing, a movement commonly observed in a multi-lane expressway.

Table 2. The top three (3) types of road crashes at NLEX (TMC, 2006)

Type of Accident Frequency % Rear-end collision 266 24 Sideswipe 206 19 Blown tire/Tire problem 179 14

Sigua (1994) established that there is general propensity for Filipino drivers to perform frequent lane changes. Palmiano, et al (2003) reinforced this observation and also implied that this behavior contributes to the observed non-lane based traffic flow in Metro Manila. In addition, the study showed empirical evidence that drivers are more aggressive and tend to perform risky lane changes even at short headways with surrounding vehicles (compared to Tokyo drivers). It is not surprising therefore that this behavior is also observed in expressway traffic.

2.4 Driver Behavior

Based on a study (Mendoza, 2004), majority of the motorists using the North Luzon Expressway are either high school graduates or high school dropouts (44% of drivers, 55% of bus drivers, and 56% of cargo truck drivers). From the same study, drivers without college degrees have significantly stronger intentions to commit violations and disregard safety precautions.

From the discussion in this section, the following are put forward as issues to address related to expressway traffic flow management and safety:  Need for appropriate setting of speed limits  Need for lane management and safe vehicle spacing  Need for information and flow management schemes that are easy to understand

3. EXPRESSWAY FLOW MANAGEMENT CONCEPTS

Speed regulation, safe vehicle spacing, and lane management are fundamental measures employed in expressways to ensure safe and efficient traffic flow. Below is a discussion of expressway flow management concepts and how they could be implemented in general.

3.1 Speed regulations

Philippine Republic Act No. 4136 (RA 4136) approved in 1964 states that: “No person shall drive any motor vehicle upon a highway at such a speed as to endanger the life, limb and property of any person, nor at a speed greater than will permit him to bring the

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

vehicle to a stop within the assured clear distance ahead. Subject to the provisions of the preceding paragraph, the rate of speed of any motor vehicle shall not exceed the following:”

Table 3. Legal speed limits, km/hr. (RA 4136) Passengers Maximum allowable speeds Motor trucks and buses Cars and Motorcycle

1. On open country roads, with no "blinds 80 50 corners" not closely bordered by habitations.

2. On "through streets" or boulevards, clear 40 30 of traffic, with no " blind corners," when so designated.

3. On city and municipal streets, with light 30 30 traffic, when not designated "through streets".

4. Through crowded streets, approaching 20 20 intersections at "blind corners," passing school zones, passing other vehicles which are stationery, or for similar dangerous circumstances.

The table has no reference to maximum speed limits along expressways since the first expressways, the NLEX and SLEX, were both constructed in the 1970s, several years after RA 4136 was approved. Moreover, there was no mention of minimum speed limits for any types of roads. Nevertheless, maximum speed limits ranging from 80 to 100kph are posted along the expressways.

As mentioned earlier, propensity for speeding, in spite of posted speed limits in NLEX underscores the need to set the appropriate speed limit for local expressways. A variety of factors are considered in setting a speed limit. These include road geometry, road crash records, legal statutes (such as RA 4136), administrative judgment, engineering judgment, etc.

Speed limits imposed in different countries vary as shown in Table 4. In some countries, the speed limit is based on the design speed which is used for the design of the different elements of the expressway. The other methodology of setting speed limits is by using the 85th percentile rule, i.e., the speed limit is set to the speed that separates the bottom 85% of the vehicle speeds from the top 15%. Drivers tend to maintain a speed that feels comfortable based on design (lane width, visibility, clearance) and use (traffic volumes, turning activity, pedestrian activity). Thus, simply reducing the posted speed limit may do very little in reducing actual travel speeds. Reducing speed may require changing roadway design or more stringent enforcement.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Table 4. Speed Limits imposed in some countries (Source: Legislative Council of Transport of Hong Kong, 1999)

Country Vehicle type car bus Truck Austria 130 100 80 Denmark 110 80 70 Canada 100-110 100-110 100-110 Germany No limit 100 80 Netherlands 120 80 80 UK 113 113 96 Slovakia 130 110 80 Hong Kong 70-110 70 70 Japan* 80-100 80 80 Malaysia* 110 80-90 80-90 Singapore * 90 60 60 US* 105-130 Restrictions only in Restrictions only in some states some states * added information; not in original source

3.2 Vehicle safe spacing/distance

There are a number of ways to check safe following distance between vehicles. Three general methods practiced are presented here: a) One meter distance for every 1kph of speed This gives a rule of thumb formula for determining the safe distance that a rear vehicle must keep from the front vehicle while cruising. For instance, a vehicle traveling at a speed of 50kph has to keep a safe distance of 50m to a vehicle in front of it. This rule of thumb is derived from the fundamental concept of maintaining safe stopping sight distance. Using this rule, calculated safe distance is more accurate for lower speeds and underestimated for higher speeds. If properly observed, this self-check could prevent situations of following too closely. b) Two-second rule The two-second rule is also used to determine a safe following distance and works this way:

Select a fixed object on the road ahead such as a sign, tree or overpass. When the vehicle ahead of you passes the object, count "one-thousand-one, one-thousand-two". You should not reach the object before you count to ‘one-thousand-two”. If you do, you are following too closely.

The two-second rule applies to your speed when you are on a good road and during good weather conditions. Otherwise, increase your distance to a four- or five-second count. c) One vehicle length for every 10kph speed Another prescribed method to check safe distance is by maintaining one vehicle length for every 10 kph of the vehicle speed as shown in Figure 4.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Figure 4. Safe distance based on vehicle lengths for 30kph and 40kph speed limits

3.3. Lane Management

Changing lane is a basic maneuver commonly observed in multilane highways including expressways. It is not considered as a bad practice in general because of the necessity in performing such maneuver in the following instances, among others: entering or exiting the expressway, following large or slow moving vehicles, lane ahead becomes blocked due to unexpected obstruction, animal on expressway, and passing.

Passing is defined here as a maneuver wherein a driver changes lane due to a slow moving vehicle in front and then returns back to his original lane. This is considered as a very dangerous move specially if done at high speed.

Frequent lane changing can happen if drivers have freedom to move about and at the same time, the vehicles can travel at any lane at any desired speed. This happens if there is a single speed limit applicable to all lanes.

Sideswiping, one of the major causes of accidents in the NLEX as mentioned earlier, is brought about by changing lanes. Regulating lane changing or encouraging drivers to keep to one lane may be the solution to minimize or eliminate sideswiping incidents.

Below are four(4) possible schemes that may be considered to achieve this objective. a) Lane segregation by vehicle type

This scheme assumes that cars and other smaller vehicles are generally faster than the larger vehicles such as buses and trucks (see Figure 5). However, this may not be true in NLEX where smaller vehicles such as the jeepneys hug the outer lane; or buses cruise fast using the inner lanes.

innerInner …lane … …outer lane

Figure 5. Lane segregation by vehicle type

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Table 5 shows the results of a speed survey conducted between the interchanges of Borol and Tabang using license plate method. It was confirmed that, in almost any given time period, buses are much faster than the other two vehicle types observed, namely, cars and trucks.

Table 5. Average Speed of Different Types of Vehicles, 2007 i) Northbound

Veh. Type Time Period car truck Bus 6-9 71.03 70.37 109.62 9-12 70.59 70.81 84.76 12-3 71.25 66.86 88.03 3-6 65.52 62.81 96.20

ii) Southbound Veh. Type

Time Period car truck Bus 6-9 68.06 60.80 89.06 9-12 64.77 64.04 92.68 12-3 73.55 70.37 75.50 3-6 84.44 71.03 89.41 b) Lane segregation by speed

This scheme introduces varying speed limits at different lanes (see Figure 6). Again, the idea is to encourage fast moving vehicles in the innermost lanes. However, the scheme does not discourage slow moving vehicles to use the inner lanes since only the maximum speed limit is set. As a consequence, faster vehicles attempt to use the outer lanes (on the right) for lane changing or passing. c) Lane segregation by vehicle type and speed

This is very similar to the first scheme (3.3-a) but with the speed limit designated in each lane (see Figure 7). Again the problem lies in the assumption that all cars or smaller vehicles travel faster than any other vehicles, which has been disproved earlier based on the result of the survey. d) Lane segregation with speed range

This is similar to the second scheme (3.3-b) but with the minimum speed limit paired with the maximum speed limit in each lane (see Figure 8). The combination of maximum and minimum speed limits results to a speed range of about 20kph, which is close to the normally accepted pace of 15kph. This assumes that the driver knows the capability/power of his vehicle and he will position himself to the most appropriate lane corresponding to his desired speed.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Figure 6. Lane segregation by speed Figure 7. Speed limit by vehicle types

Figure 8. Lane segregation with speed range

4. SPEED AND HEADWAY ANALYSIS

4.1 Speed limit determination

Table 6 shows the stations where data are available for speed analysis. It shows three locations representing varying cross sections or number of lanes.

Based on the speed frequency distribution, the 85th and 15th percentile speeds representing maximum and minimum speed limits, respectively, are determined. S-curves of cumulative frequency distribution are shown in Figure 9 to 11. For the determination of maximum speed limit for instance, the value of 85th percentile is identified on the vertical axis. A horizontal line is drawn until it crosses the S-curves. The required speed limit for a specific lane is the value of speed on the horizontal axis when a vertical line is drawn from the intersection of the S-curve and the 85th percentile line.

Table 7 shows the summary of the computed 85th and 15th percentile speeds. It will serve as basis for the determination of speed limits.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Table 6. Location for speed studies Statio Location No. of lanes Period of observation n per direction (year 2007) TS6 Meycaucayan – Marilao 4 lanes Jun 7, 15:52:11 to Jun 8, section 7:21:00 TS10 Burol – Sta. Rita 3 lanes NB: Jun 7, 10:49:12 to section 13:39:27 SB: Jun 7, 11:28:07 to 16:50:26 TS12 Sta. Rita – 2 lanes Jun 6, 19:49:25 to Jun 7, section 9:07:53

100.00

90.00

80.00

70.00

60.00 NB_slow NB_mid1 50.00 NB_mid2 40.00 NB_fast CumulativeFreq. 30.00

20.00

10.00

0.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 Speed

Figure 9. Speed cumulative frequency distribution, 4 lanes

100.0

90.0

80.0

70.0

60.0 NB_slow 50.0 NB_mid 40.0 NB_fast

30.0 Cumulative Freq. Cumulative 20.0

10.0

0.0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 Speed

Figure 10. Speed cumulative frequency distribution, 3 lanes

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

100.0

90.0

80.0

70.0

60.0 SB_slow 50.0 SB_fast 40.0

30.0 Cumulative Freq. Cumulative 20.0

10.0

0.0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 Speed

Figure 11. Speed cumulative frequency distribution, 2 lanes

Table 7. Summary of 85th and 15th percentile speeds (km/h) 4-lane 3-lane 2-lane

Slow Mid 1 Mid 2 Fast Slow Mid Fast Slow Fast P15 54 61 71 82 61 82 91 52 67 P85 82 89 99 107 88 111 115 93 110

4.2 Headway analysis

The propensity for tailgating or unsafe driving characterized by following too close to the vehicle ahead can be verified by analyzing the time headway distribution based on available data. The tables below show the percentile values of headways maintained by vehicles traveling at speeds equal to 100 km/h or higher.

100.00

90.00

80.00

70.00

60.00 mid 50.00 fast 40.00

30.00 Cumulative Freq. 20.00

10.00

0.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Time Headway, sec.

Figure 12. Time headway for fast and middle lanes, northbound direction

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

Figure 12 shows the cumulative distribution for both the middle and innermost lanes. Under the ‘1 meter distance for every 1kph speed’ rule, the equivalent safe time headway required is 3.6 sec. For the middle lane, about 16% of those traveling at 100kph or faster have ‘unsafe’ headway. In the faster lane(innermost lane), about 20% of those traveling at 100kph or faster have ‘unsafe’ headway of less than 3.6 sec.

5. DISCUSSION AND RECOMMENDATIONS

From the analysis of speed and headway distributions the following could be put forward as recommendations.

5.1 Speed Limit

If a single speed limit is to be imposed, the proposed values should be:  Maximum speed limit: 110kph.  Minimum speed limit: 50kph.

For varying maximum speed limits to be imposed at specific lanes, the proposed values are shown in the succeeding tables (Tables 8-10).

Table 8. Proposed Speed Limits (km/h): 4 - lane

Fast Mid2 Mid1 Slow

110 100 90 80

Table 9. Proposed Speed Limits (km/h): 3-lane Fast Mid Slow 110 100 90

Table 10. Proposed Speed Limits (km/h): 2-lane

Fast Slow 110 90

Currently, speeds of 100 and 60kph are imposed for maximum and minimum speed limits, respectively. A revision on this regulation is therefore necessary.

5.2 Lane management

Several options were put forward for lane management, namely, (1) lane segregation by vehicle type, (2) lane segregation by speed, (3) lane segregation by vehicle type and speed, and (4) lane segregation with speed range.

From the cognitive perspective, lane segregation by speed (option no. 2) is recommended for it is the least complex in terms of information and rules that must be complied with. The maximum speed should be indicated. If properly enforced, this will reduce risk taking behavior

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011 since the perceived risk for violating the regulation will be higher than the target risk. However, in the information materials that will be distributed, it is important to indicate that the minimum speed is the maximum speed of the adjacent lane. Again, if under speeding is properly enforced, this will force slow moving vehicles to use the outermost lanes.

5.3 Checking Vehicle Distance

To address the issue of tailgating which is the main cause of rear-end collision accidents in the expressway, a scheme that will enable drivers to check their running distance from the from front vehicle could be implemented (as discussed in section 3.2).

The proposed layout for this scheme is shown in Figure 13. Preferably, this self-check should be installed every 10km. An advanced information sign must be placed well ahead, say 500m from the ‘self-check’ location. The scheme must be introduced and presented to road users using flyers and tabloids issued regularly by TMC.

Figure 13. ‘Check your distance’ layout and advanced information sign

To improve compliance with the recommended scheme to prevent tailgating, it is of paramount importance to ensure that the message and language used in the traffic signs that will be put up are easily understood by drivers. The 500-m sign is intended to inform the motorists of the start of the self-check line so that they can start adjusting driving pattern.

Proceedings of the Eastern Asia Society for Transportation Studies, Vol.8, 2011

6. CONCLUSION

The paper has addressed the issues related to safety along expressways in the Philippines. Although most of the data are gathered for the NLEX, the same driver behavior and therefore, the same concepts and recommendations may be applied to the other expressways. In addition to the recommendations given, it is necessary that uniformity in traffic management be practiced in all expressways to instill better behavior among all road users.

REFERENCES

ALMEC, Metro Manila Urban Transportation Integration Studies, 2000.

Inquirer, “From SCTEx to Star”, http://opinion.inquirer.net/inquireropinion/talkofthetown/ view/20100905-290594/, accessed September 28, 2010.

Legislative Council of Transport of Hong Kong, 1999

Mendoza A, A Study On Motorists’ Perception of and Experience with PNCC’s NLE Operating Personnel’, 2004.

Palmiano HSO, Ueda S, Yai T, and Fukuda D, Development of a simulation system for jeepney stop vicinity located in front of shopping center, Journal of the Eastern Asia Society for Transportation Studies, Vol.5, October 2003.

Republic Act No. 4136, “An act to compile the laws relative to land transportation and traffic rules, to create a land transportation commission and for other purposes”, 1964.

Sigua RG, Traffic characteristics of major arterial roads in Metro Manila, Proceedings of the 1st Regional Symposium on Infrastructure Development in Civil Engineering. Bangkok, Thailand, 1994.

Tollway Management Corporation (TMC), Traffic and accident report, 2006.