Passing Lane Research
New Zealand’s topography and distance between major urban centres creates some unique considerations for our road network. In the future over 1000km of our two-lane rural state highways will lie within in the high volume range: 10,000 to 25,000 AADT. At these volumes it is not ideal to treat passing lanes as isolated facilities; preferably they should be considered as a route treatment in series. This raises a number of questions;
- What are the safe and robust design principles for placing passing lanes in series along a high volume route?
- Are there safety concerns at passing lane merges at higher volumes? And/or are there operational issues at higher volumes?
- Can treatments such as ITS traffic control systems be applied to prolong the life of passing lanes and delay the requirement for 4-laning?
- What is the optimal benefit to cost compromise between the length of the passing lane, and the spacing between passing lanes? How do length and spacing interact?
- How do you evaluate economic measures for placing passing lanes along a route?
- What tools are best placed to answer these questions? And how are these answers succinctly communicated to traffic engineers to ensure the balance between common protocol and site-specific issues is maintained?
Traffic Design Group (TDG) has recently completed research in collaboration with the NZ Transport Agency investigating these questions in detail. The research focused around developing, implementing and measuring safe and robust design principles and techniques to understand economic efficiency and operation on New Zealand’s highways with a focus on passing lanes and 2+1 passing facilities.
The research built on existing local and international knowledge, captured key observed data in order to develop an understanding of on-road behaviour and the operational characteristics, identify the core components of economic costs and savings, establish principles for measuring the optimal economic return from the length and frequency, and evaluate the potential benefits of ITS design treatments of passing facilities.