Capacity per traffic lane using express coach
December 9, 2010 Leave a comment
The maximum throughput of a single motorway lane is currently about 1,800 vehicles per traffic lane per hour (based on the Highway Code 2 second rule) with a throughput of people of about 2,880 (based on average occupancy of 1.6 people per vehicle). Let’s compare this a system based on express coaches with an average occupancy of 30 people (current average occupancy of a coach on the National Express network) and a more cautious 4 second spacing between vehicles which allows for a throughput of 27,000 people per traffic lane per hour. Using larger 87-seater double-decker coaches (as used on the Oxford-London route) and yield-management fares (which would increase occupancy to more like 80%) the throughput would be increased to 63,000 people per single traffic lane per hour. Using these available technologies a single lane of a motorway would be able to carry three times more people than on 20 lanes of traffic using private cars at low occupancy.
The effectiveness of coach lanes is demonstrated by the M4 bus lane, which used to carry 21% of the people entering London on the route but which was which was suspended because it was ‘virtually empty’ even though taxis and motorcycles were also allowed to use the lane.
It is unfortunately that this opportunity to ‘sweat the assets’ of our motorway network has being ignored to date. One of the key arguments in favour of High Speed 2 is that there is not sufficient capacity on the roads. High Speed 2 will initially offer four trains an hour with 1,100 seats per train and will therefore only provide 4,400 additional movement per hour. Plans to realign the A14 and to build the ‘Lower Thames Crossing‘ are also based on the assumption that the current roads are operating at capacity. It is of concern that a key recommendation relating to the recent widening of the M25 was that a strategic express coach system should be developed to avoid this additional traffic capacity being absorbed by greater private car use. This strategic coach system has not been developed and the government is now discussing addressing other ‘pinch points’ on the M25.
The government is supporting ‘vehicle platooning’ that allows cars follow each other more closely. No one seems to be predicting exact what increase in traffic flow rates will be achieved other than to say that “the utilisation of existing road capacity will also be increased with a potential consequential reduction in journey times”. The EU is currently funding a project called ‘Safe Road Trains for the Environment‘ which is January 2011 allowed a single vehicle to follow feet behind a truck. Let’s be generous and assume that it will double throughput to one vehicle per second resulting in 5,760 people per traffic lane per hour which is still way below what can be achieved with today’s express coach technology. The researchers claim that this convoying system will allow drivers to ‘read, rest, eat, make phone calls, and so on’ but this is of course exactly what people are already doing in express coaches!
Coach systems of this sort also achieves huge energy saving compared to the car and fares would be much lower that the cost of rail and the private car. It allows people to work and rest while traveling which benefits ‘productivity’ which is one of the reasons the government gave for increasing motorway speed limits.