Evaluation of the "Keep Left Unless Overtaking" Regulation Evaluation of The
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EVALUATION OF THE "KEEP LEFT UNLESS OVERTAKING" REGULATION EVALUATION OF THE "KEEP LEFT UNLESS OVERTAKING" REGULATION GR 89-2 INDU ZUTSHI ANTONIETTE CAVALLO VIC ROADS SEPTEMBER 1989 ACKNOWLEDGEMENTS: The advice of Max Cameron and David Healy with the data analysis is gratefully acknowledged. REPORT DOCUMENTATION PAGE Report No. Report Date: ISBN Pages GR 89-2 September 1989 o 7241 7342 0 58 Title and Sub~title: EVALUATION OF THE "KEEP LEFT UNLESS OVERTAKING" REGULATION Author(s) Type of Report: INDU ZUTSHI GENERAL REPORT ANTONIETTE CAVALLO Performing Organisation(s) ROAD SAFETY DIVISION VIC ROADS 290 BURWOOD ROAD HAWTHORN VIC 3122 AUSTRALIA Abstract: On 1 March 1988, a regulation was passed which made the previously advisory 'Keep Left Unless Overtaking' (KLUO) zones (indicated by signs) regulatory. These signs are placed only on high-standard sections of urban and rural freeways and divided arterial roads in rural and "outer" urban areas where there is a limited need to be in the right hand lane for right turns, parking and standing in the left lane is also not allowed, and where moderate traffic volumes prevail. Signs are also located where climbing and overtaking lanes are provided. This study examined whether there were any effects of the regulation and accompanying publicity and enforcement on driving behaviour at freeway and divided arterial road locations throughout Victoria. There was a significant increase in the proportion of cars travelling in the left lane after the regulation was introduced. Specifically, there was a 3.6% increase at KLUO zones and a 5.0% increase at similar locations where KLUO zones do not apply, for cars overall. For free speeding cars there was an increase of 7.4% in left lane usage where advisory KLUO zones became regulatory and a 12.0% increase at similar locations where KLUO zones do not apply. A marginal increase was detected for trucks, the majority of which already travel in the left lane (almost 90%). Two factors were found to be associated with left lane usage. The increases in left lane usage is characteristic of motorists who drive at/or below the speed limit. Additionally, the traffic volume on a route is directly related to the degree of left lane usage. Key Yards: Disclaimer: (IRRD except where marked*) This report is disseminated in traffic regulations, traffic signy traffic the interests of information exchange. larte, driving (veh), car, lorry, overtaking,The views expressed are those of the lane usage*, traffic",survey, keep left*, author, and not necessarily those of Victoria* VIC ROADS. Reproduction of Form and completed page is authorised. ( i ) EXECUTIVE SUMMARY On 1 March 1988, a regulation was passed which made .the previously advi sory 'Keep Left Unless Ove rtaking' (KLUO) zones (indicated by signs) regulatory. This regulation followed from a recommendation by the Task Force who developed the Speed Management Strategy for Victoria. These signs are placed only on high-standard sections of urban and rural freeways and divided arterial roads in rural and "outer" urban areas where there is a limited need to be in the right hand lane for right turns, parking and standing in the left lane is also not allowed, and where moderate traffic volumes prevail. Signs are also located where climbing and overtaking lanes are provided. This study examined whether there were any effects of this regulation on driving behaviour at freeway and divided arterial road locations throughout Victoria. To measure these effects the volume and speed of traffic in the right hand and left hand lanes on a sample of sites were measured before and after the introduction of the regulation on 1st March 1988. A major publicity campaign was_involved at the same time which ran for a period of 5-6 weeks during February and March 1988, in both the Metropolitan and Regional areas of Victoria. Police enforcement of the regulation also accompanied publicity and legislation. The results have been categorised by cars and trucks, for all vehicles combined and separately for vehicles travelling at free speeds. Results of the study suggest that there was a significant increase in the proportion of cars travelling in the left lane after the regulation was introduced. Speci fi cally, there was a 3.6% increase at KLUO zones and a 5.0% increase at similar locations where KLUO zones do not apply, for cars overall. For free speeding cars there was an increase of 7.4% in left lane usage where advisory KLUO zones became regulatory and a 12.0% increase at similar locations where KLUO zones do not apply. A marginal increase was detected for trucks, the majority of which already travel in the left lane (almost 90%). Two factors were found to be associated wi th left lane usage. The increases in left lane usage is characteristic of motorists who drive at/or below the speed limit. Addi tionally, the traffic volume on a route is di rectly related to the degree of left lane usage. These findings provide valuable information for future consideration. Firstly, publicity relating to 'Keep Left Unless Overtaking' needs to address two separate driver groups: those who are law-abiding with respect to speed and those who do not observe speed limits. The location of KLUO zones should take into consideration traffic volumes and saturation levels on a route. (ii) The increases observed in the study are characteristic of sites where there is little or no opportunity for right hand turns, parking/standing on the left lane is prohibited and an uninterrupted dual carriageway is available. The results may not be generalizable to locations where such conditions are absent. The results of the study also suggest that publici ty was important in influencing the observed change in behaviour, given the large increase in left lane usage at non-KLUO sites. However, it is not possible to attribute the effect sOlely to publici ty since the presence of KLUO zones and enforcement may have promoted a generalization of left lane usage behaviour. The significantly greater increase in left lane usage experienced at non-KLUO zones (for free speeding cars) may be explained by the greater scope for a potential increase at these sites since left lane usage by free speeding cars was ini tially much lower than at KLUO zones where signs had previously operated in an advisory capacity. TABLE OEL CONTENTS PAGE . --" EXECUTIVE SUMMARY ( i ) LIST OF TABLES (iii) LIST OF FIGURES (v) 1.0 INTRODUCTION 1 2.0 STUDY DESIGN AND DATA COLLECTION 2 3.0 ANALYSIS 4 3.1 Preliminary Analysis 4 3.2 Analysis Issues 4 3.3 Significance Tests 5 3.3.1 Overall Effects of the KLUO Regulation 5 3.3.2 Comparative effects of the KLUO Regulation 5 4.0 RESULTS 6 4.1 Overall Effects 6 4.2 Effects due to Presence of KLUO Signs 7 4.3 Effects at 3 Laned site 21 4.4 Detailed Results 22 4.5 Significance Tests 25 5.0 DISCUSSION 28 6.0 CONCLUSIONS 30 REFERENCES 32 APPENDICES A Site Descriptions 33 B Frequency Distributions 39 c Data Analysis for Individual Sites 46 2 D 2x2 X Test 51 (iii) LIST OF TABLES TABLE PAGE 1 Sampling Schedule Before and After Introduction 3 of the Regulation 2 Lane usage and Mean Speeds for All Vehicles for All 2 Lane Sites 6 Lane Usage and Mean Speeds for Vehicles Travelling at Free Speeds for All 2 Lane Sites 7 4 Lane Usage and Mean Speeds for All Vehicles for Sites with and without KLUO Signs 12 5 Lane Usage and Mean Speeds for Vehicles Travelling at Free Speeds for Sites with and without KLUO Signs 12 6 Lane Usage and Mean Speeds for Princes Highway west at 17 km Post - 3 Lane Each Way 21 7 Lane Usage and Mean Speeds for princes Highway West at 17 km Post for Vehicles Travelling at Free Speed 22 8 Lane Usage and Mean Speeds for All Cars at Each Site 23 9 Lane usage and Mean Speeds for All Trucks at Each Site 24 10 Calculated X2 Values 25 11 Best Model Fit Using GLIM 27 12 percentage increase in left lane usage at signed and unsigned sites for all cars and cars travelling at free speeds only and difference in % change 28 B.1 Total Volumes by Vehicle Type by Lane and by Speed 40 B.2 Total Volumes by Vehicle Type by Lane and by Speed for Vehicles Travelling at Free Speeds 41 B.3 Total Volumes for Sites with KLUO signs by Vehicle Type by Lane and By Speed 42 B.4 Total Volumes for Sites without KLUO Signs by Vehicle Type by Lane and by Speed 43 B.5 Total Volumes for sites with KLUO Signs by Vehicle Type by Lane and by Speed for Vehicles Travelling at Free Speeds 44 B.6 Total Volumes for Sites without KLUO Signs by Vehicle Type by Lane and by Speed for Vehicles Travelling at Free Speeds 45 (iv) C.1 Lane Usage and Mean Speeds for All Cars Combined on 2 Lane Highways 47 C.2 Lane Usage and Mean Speeds for All Trucks Combined on 2 Lane Highways 48 C.3 Lane Usage and Mean Speeds for Cars Travelling at Free Speeds on 2 Lane Highways 49 C.4 Lane Usage and Mean Speeds for Trucks Travelling at Free Speeds on 2 Lane Highways 50 (v) LIST OF FIGURES FIGURE TITLE PAGE 1 Cars - Left Lane - Total 8 2 Ca:rs - Right Lane - Total 8 3 Trucks - Left Lane - Total 9 4 Trucks - Right Lane - Total 9 5 Cars - Left Lane - Free Speeds Only 10 6 Cars - Right Lane - Free Speeds Only 10 7 Trucks - Left Lane - Free Speeds Only 11 8 Trucks - Right Lane - Free Speeds Only 11 9 Cars - Left Lane - Sites with KLUO Signs - Total 13 10 Cars - Right Lane - Sites with KLUO Signs - Total 13 11 Cars - Left Lane - Sites without KLUO Signs - Total 14 12 Cars - Right Lane - Sites without KLUO Signs - Total 14 13 Trucks - Left Lane - Sites with KLUO Signs - Total 15 14 Trucks - Right Lane - Sites with KLUO Signs - Total 15