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Congestion and Bus Services

The following article has been written by Peter Osmon FIET, and was submitted for publication on 20 August 2018.


Efficient and reliable bus services are important to London’s economy and to the many Londoners who use them every day: but the traffic congestion, due to moving and parked vehicles, encountered by buses can double journey times and many thousands of hours of Londoners’ lives are wasted every day due to service delays attributable to congestion. Our buses share road space with great numbers and varieties of other vehicles. Resulting congestion negates the reliability and ups the cost of providing bus services. Private cars are the most obvious source of this congestion. But a full quantitative treatment could attribute bus service delays to all the various categories of vehicular traffic.

Technological changes- App cab services, Internet shopping deliveries and the favourable economics of electric cars- are new and growing sources of increased traffic congestion- further damaging to the cost of and reliability of our bus services.

What is to be done about London’s congested bus routes?

Measures which would give more road space priority to buses, including extending bus lanes, could shift some of the congestion burden from buses onto private cars. The Mayor needs additional powers to counter the threats from technological change to bus services. The author favours regulation of Internet delivery services to minimise interference with other traffic and TfL taking over provision of App cab services to provide a premier class point-point passenger service alongside London’s standard class bus service.

Traffic congestion encountered by buses can double journey times

Reducing this congestion would improve bus services, with consequent service cost/revenue benefits, as this example shows.

Consider a hypothetical bus route comprising 16 stages with service intervals of 8 minutes. Suppose an average stage duration of 4 minutes during the peak and 3 minutes off-peak. Then, during the peak, a bus travels the route (in one direction) in (4 x 16) = 64 minutes and 64/8 = 8 buses are needed to maintain the service in each direction: 2 x 8 = 16 buses in total. Off-peak only 2 x (3 x 16)/8 = 12 buses are needed.

More generally, if congestion induced delay can be reduced by N%, then the number of buses needed to maintain the service level is reduced by N%. Alternatively, the same number of buses can provide a service with N% shorter intervals- less crowded buses likely attracting (some) more fare paying passengers.

Incremental reductions in congestion would generate these benefits incrementally.

Sources of congestion

Bus services are affected negatively by two kinds of vehicular congestion: dynamic- slow moving traffic on crowded roads; static- waiting or parked vehicles restricting the capacity of the roadway. Evidently dynamic congestion is responsible for longer bus journey at peak traffic compared with off-peak, whereas static congestion is a more constant factor- extending journey times throughout the day.

London’s bus routes are carried by a variety of roads, reflecting the historical incremental development of our city, and which are more or less fit for the purpose. The variety of congested routes is exemplified by conditions along three Inner NW London roads:

A41: a relatively modern 4 to 6 lane radial road, with significant congestion only at peak times.

A5: an ancient 3 to 4 lane radial road, with significant congestion along its length, especially but not only at peak times.

A407: an old 2 to 3 lane orbital road, frequently congested and with tailbacks at approaches to intersections.

Road space occupancy of bus travel per person compared with car travel

An example illustrates this issue. Compare the road space occupancy per person of a 5m long bus with 30 passengers and a 3m long private car transporting just its driver-

(a) Both vehicles stationary: (30/15 = 2 persons per metre of road) compared with (1 person per 3m of road): bus travel makes 6x better use of precious road space

(b) Both traveling at 15 km/h and separated by stopping distance of 10m: 30 persons per 25m of road compared with 1 person per 13m of road- bus require 30/25 = 1.2 person per metre of road, whereas car travel requires 13m of road per person: the moving bus makes more than 10x better use of road space.

Evidently there is an efficient-use-of-scarce-road-space case for giving buses priority over cars. We are already accustomed to giving buses a degree of priority by means of bus lanes, but this priority is nowhere proportional to the factor ten that fairness would imply.

More road space priority for buses would shift some of the congestion burden from buses onto private cars (and some motorists might then choose to use public transport instead of their cars):

Currently, buses and private cars share the roadway along bus routes, with buses having a degree of priority by means of bus lanes. Some further measures that would provide additional road space priority for buses are as follows.

Extension of Bus lanes:

so they are operational for more of the day

so they extend fully up to intersections.

Introduce Bus lanes:

into 3-lane roads at the approach to intersections.

Smart traffic light control:

Lights turn green for buses as they approach intersections

Respect for bus priority:

Require other vehicles to give way to buses at intersections etc.

Require other vehicles to maintain good lane discipline alongside bus lanes.

Enforcement of the above using video cameras installed on the sides and front of buses together with automatic number-plate identification and prosecution- as with Congestion Zone Charging- would surely be economical and effective. Revenue from fines would likely more than cover the cost of these measures.

New contributions to congestion, consequences of Londoners’ adopting new technologies, threaten the future reliability of bus services: the rapidly increasing road traffic related to Internet/WiFi enabled services- cabs and retail deliveries, and the attractions of electric motoring. These will have to be managed.

Managing the volume and behaviour of “cab” traffic

There is a legitimate demand for a “premier” passenger transport service in London- speedier than buses and also point-to-point: cabs. Increased pressure on road space for private cars would increase demand for the service. But unless the increasing use of cabs is carefully managed, cab traffic will contribute significantly to congestion. According to the Guardian 16/08/2018 there are now 45,000 drivers in the capital working for Uber alone, and the Mayor does not have power to cap the number. Ideally cabs should not be permitted to cruise or otherwise travel needlessly to collect passengers, although there is a case for them to use bus-lanes. If the mayor had the necessary powers, a system of widespread small cab ranks, and a fleet of licensed radio-controlled cabs, centrally managed by an optimising algorithm, could ensure an efficient cab service that contributed minimally to congestion. In the opinion of the author the best way forward would be for TfL to have this management role, with license fees potentially providing a source of direct subsidy for the higher passenger volume “standard class” bus services.

Management of retail delivery traffic

Londoners are increasingly shopping on-line from home, with next-day or same-day delivery (and often return) of purchases, to home or workplace by courier, and consequent reduced demand for bus services to shopping centres. In another context this exponentially growing habit is called “the death of the high street”. The volume of courier cars and vans on London streets must already be making a significant contribution to traffic congestion- and “we ain’t seen nothin’ yet”! How to control it without overmuch reducing end-user benefit?

On-line retailers (Amazon et al) have their warehouses outside London and transport Londoners’ purchases to distribution points within London where they are transferred to couriers for delivery. From the viewpoint of road-usage efficiency, with multiple on-line retailers and multiple courier companies, there is much journey duplication: needless traffic- and some similarity to the cab traffic management problem just discussed.

Centralised management, like the solution proposed for cab traffic, seems necessary to overcome journey duplication, and the Mayor needs the powers to impose this.

There is also some similarity to Royal Mail’s situation, who are of course one of the courier companies: mostly delivering smaller and lighter than average items. Royal Mail’s couriers are postmen pushing carts full of letters and packets along the footpaths. Retailers’ own couriers’ deliveries tend to be spaced out, and powered carts would be more appropriate. If these used the footpaths, as disabled and baby buggies do, and cycle paths, potential congestion increase could be transferred from the roadway to where it might be more readily absorbed.

Electric cars are displacing diesel and petrol driven cars

Electric cars have lower running costs- because they are more efficient and because electricity is cheaper (there is no excise duty or VAT). Charging using off-peak electricity is especially economical. These factors will surely prompt more motorists- perhaps especially commuters- onto London’s roads. How can this source of additional congestion be countered- unless by road space charging and additional priority for buses?

Importance of data

Private cars, cabs, and delivery vehicles have been highlighted above as a sources of bus-service impeding congestion. Detailed analysis of static and dynamic congestion causes would allow a fuller treatment, with quantitative attribution of the characteristic contributions of all vehicular traffic categories to delays in bus services and development of effective measures to protect and improve London’s Bus Service.

Peter Osmon FIET