Review of the red to green sequence at traffic signals.

The UK Department for Transport commissioned TRL to review the omission or reduction of the 'starting-amber' (the red-with-amber shown before the green) in the traffic signal sequence, both in efficiency and safety terms, compared with the current policy. project and some preliminary findings. Note that any views expressed are not necessarily those of the Department for Transport.r signal denotes an impending change to green, but conveys the same prohibition as the red signal. In the UK the length of the period is fixed at two seconds. y with the two second starting amber is low. On average the front vehicle started to move 0.25 seconds before green and crossed the stopline 0.38 seconds after the green. There was a tendency for a proportion of drivers to treat the starting amber as a signal to go. Just over a third of vehicles that waited on or behind the stopline had crossed the stopline (front wheel) before the start of green, and 4 and 17 percent after 1 and 1.5 seconds starting amber respectively. Motorcyclists had the highest rates with approximately three quarters crossing the stopline before green. At junctions the front vehicle moved an average of about one metre and was over three quarters of a metre in advance of the stopline by the start of green. However, drivers tended to treat the situation with more caution when there was a potential conflict, or poor intervisibility with opposing movements. There was no indication that the current recommended UK intergreen times are insufficient given current driver behaviour in the starting amber. And investigations of previous accident studies at traffic signals did not identify a safety related problem associated with the starting amber. The driving simulator experiment indicated that omitting the two second starting amber would increase the time relative to the start of green when vehicles cross the stopline by an average of 1.6 seconds for younger drivers (less than 55 years old) and 1.2 seconds for older drivers. The difference in ages appears to be largely due to more younger drivers starting to move in the red-with-amber when it was set to 2 seconds. Reducing the amber to one second was found to increase the average time for younger drivers crossing the stopline by about 0.7 seconds. The results were similar for vehicles approaching the stopline and indicated that the starting amber can be beneficial to maintain progression at closely spaced signals. These increases in starting delay would tend to reduce junction capacity if existing intergreen times are maintained (the consequences for intergreen times are yet to be assessed). Driver questionnaires indicated that the removal of the starting amber results in a signal change that is easier to understand, but made drivers feel more hurried in their decisions, which could have safety implications. Pedestrians consider that they would feel less safe if the starting amber was removed and would show more caution and request pedestrian phases more often. This could possibly cause greater delays to pedestrians and traffic, but could have a positive influence on pedestrian safety For the covering abstract please see ITRD E135207.