EEM1 (road infrastructure) Appendix 7 - Passing lanes

Introduction

This appendix contains procedures to evaluate the benefits of providing passing lanes, typically through the provision of passing lanes, climbing lanes, slow vehicle bays, and increases in the natural passing opportunities from improved alignments

Benefits of providing increased passing lanes

A wide range of vehicle types travel on New Zealand highways each day and inevitably some slower vehicles impede other faster vehicles. In order to overtake these slower vehicles on two lane highways, drivers must use the opposing traffic lane. However this is not always possible or safe. Suitable gaps in the opposing traffic may be limited and the road alignment may restrict the forward sight distance. The result is increased travel times as well as increases in driver frustration. Research suggests that the latter may lead to an increase in unsafe passing manoeuvres and accidents (Thrush, 1996).

Passing lanes

Passing lanes (and climbing lanes) provide a relatively safe environment for vehicles to overtake other vehicles, allowing them to travel at their desired speed until such time as the platoons reform. As a consequence the benefits of passing lanes generally extend much farther than the physical length of the passing lane section itself, as shown in figure A7.1 below.

Figure A7.1 Benefit length of installing passing lanes

Passing lanes free impeded vehicles from slow moving platoons and in doing so they improve levels of service, reduce travel times and driver frustration. These benefits will be greatest at locations where road and traffic conditions result in significant passing demand.

Other improvement options

In hilly and mountainous terrain, passing lanes (and climbing lanes) may not be viable, particularly on lower volume roads. In such cases other improvement options such as slow vehicle bays and shoulder widening should be considered. The benefit of full length passing lanes in less severe terrain can also be low, when traffic volumes are low. In such cases improving sight lines through clearance of vegetation and vertical or horizontal realignment may increase the available passing opportunities and generate other safety benefits.

Passing lane evaluation procedures

There are three procedures in this appendix.

• passing lane strategy for determining the location of individual passing lanes (appendix A7.3).
• assessment of individual passing lanes identified as feasible from a passing lane strategy (appendix A7.4).
• detailed analysis of passing lane projects using rural traffic simulation software, such as TRARR (appendix A7.5).
• Figure A7.2 should be used to determine the appropriate procedure.

Figure A7.2 Selection of passing lane analysis procedure