Right Turn On Red

an analysis of the advantages and disadvantages of allowing 'turn right on red'

Introduction

This chapter of the web site investigates the advantages and disadvantages of permitting 'turn right on red' at road junctions. This manoeuvre is permitted at many signalised junctions in the USA, Canada and the Middle East, but not in Europe (except Germany). In the UK (where vehicles drive on the left), the equivalent manoeuvre would be 'left turn on red'.

Right Turn On Red

Figure 1 shows the 'right turn on red' manoeuvre, at a signalised junction. The junction has four approach arms, and the east-west axis currently has a green light. Traffic flows freely in the east-west direction. Meanwhile, the white car waiting at the southern approach wishes to turn right. If the 'right turn on red' rule applies, the white car can turn through the junction (even though the traffic light is set at red) when a gap in the west-to-east flow occurs, although in the USA the car must by law stop at the stop line, before moving on. This means that an increased traffic flow is possible, compared to the European style where the white car would have to wait.


Figure 1: The 'Right Turn On Red' manoeuvre

Advantages of Right Turn On Red

There are two major advantages to 'turn right on red'. Firstly, the fact that more traffic can flow every hour increases the capacity of the junction. Secondly, the vehicles which are turning are not idling their engines, and needlessly causing emissions.

Tables 1 through 3 show the possible combinations of vehicles waiting at the southern arm of the junction, depending on the number of lanes provided. It is assumed that 25% of the traffic wishes to turn left, 50% want to go ahead, and 25% of the traffic wishes to turn right. Vehicles turning right can only do this on a red light, if the vehicles in front have turned right first. (A=ahead, R=right, L=left, AL=ahead/left)


Table 1: Right turn on red - 1 lane


Table 2: Right turn on red - 2 lanes


Table 3: Right turn on red - 3 lanes

As the number of lanes increases, the number of vehicles able to turn right on red goes up sharply, as shown in Table 4. Where a lane holds traffic making different movements, traffic which isn't going right blocks the traffic which wants to do so.This is why it is more popular in the USA and Canada, since roads in these countries have more lanes, with separate turning movements, and can therefore make better use of this technique.


Table 4: Results of the right turn of red technique

In the USA, right turn on red is used to save fuel, and federal assistance requires the use of right turn on red, where practical.

Channelisation

In the Middle East, an alternative method is 'channelisation', which increases the possible traffic flows. The general design is shown in Figure 2. Traffic moves ahead or turns left at the junction, whereas traffic turning right moves along the curved roads linking the arms of the junction. As long as the queue at the junction does not extend back past the start of the channelisation, right-turning traffic can flow freely, with a flow rate about ten times greater than right turn on red - a significant benefit. Once the queue extends back past the start of the channelisation, then the channelisation behaves in the same way as 'turn right on red' at the stop line. If the radius of curvature of the channelisation is 30m (a typical value) then at 6m per vehicle, a queue of only five vehicles is sufficient to reduce channelisation to the efficiency of right turn on red. If this happens consistently, then the start of the channelisation needs to be extended back past the end of the queue.


Figure 2: Channelisation

Disadvantages of Right Turn On Red

There are two disadvantages to right turn on red. Firstly, there is the question of pedestrian safety. Will the cars yield to pedestrians when the pedestrians are crossing? Secondly, if the car at the stop line doesn't want to turn right, which is their right, will the car drivers further back be patient?

The US ITE (Institute of Transportation Engineers) conducted a survey into the effects on pedestrian safety. Surprisingly, it found that the number of pedestrian accidents went down. This is probably because the vehicle has to stop at the stop line, and therefore the cars are moving slowly. Despite this, there are other effects, such as pedestrians giving way to right-turning cars, even when the pedestrians have right-of-way.

A car at a junction which permits right turns on red may turn if the driver feels that it is safe to do so. As a consequence, car drivers are sometimes abused by car drivers behind them who also wish to turn right on red.

Conclusions

Right turn on red, as a practice:

Right turn on red is an approach that is not used very much in the UK. The roads in the UK have fewer lanes than in the USA - and so the benefits of it are not as great as they would be in the USA.