Twice green despite negative impact on emissions
A double provision for cyclists at traffic lights does have a negative impact on emissions and air quality at intersections. The increased contribution by traffic to these concentrations is however small and usually does not cause additional air quality problems.
Twice green means cyclists receive a green light twice within a single complete traffic light cycle. CROW research institute has calculated the impact of changes in traffic light management or replacing traffic lights by roundabouts for a number of intersection situations in the recent publication ‘Kruispunten en Luchtkwaliteit' (Publication 218i). According to traffic light expert Bo Boormans of DTV Consultants twice green remains the most obvious way of reducing waiting times for cyclists. 'Twice green can be implemented on virtually all intersections. I think waiting times – outside peak hours anyway – for bicycles may be reduced to 60 per cent in virtually all instances. Breda, for example, has had active and successful policies in effect since 1998 to significantly reduce waiting times for cyclists by means of, among other measures, double green stages, if need be at the expense of waiting times for car traffic. It is however important that a choice is made, and it is not submissively accepted that extra room in traffic light settings is automatically awarded to car traffic.' The CROW leaflet, too, states that it should be taken into consideration that twice green is promoted as a way to increase bicycle use, which may lead to an overall positive impact on air quality.