Figure 1: Site location
The Lincoln Tunnel in the USA has very high traffic flows. This has led Paul Withrington of Transport Watch to suggest that the strategy of replacing trains with buses would be the right thing to do. This policy was very popular in the past.
Not everyone is convinced that this is the right approach. Another web-site called 'SpeedLimit', otherwise largely about cars, holds the contrary opinion.
This chapter attempts to address the issue by examining one location in the UK, on the busy rail line through Bath. By considering the geometry of the bridge and station at this point, the feasibility of conversion from rail to buses can be established.
The location of the site is shown in Figure 1. The railway tracks can be seen running horizontally through the centre of the figure.
Figure 1: Site location
Figure 3 shows a photograph of the bridge, indicating the shape of the bridge. This then enables a scale drawing to be produced, as is shown in Figure 4. Two dashed rectangles are also shown, which are 7m and 9m across. This corresponds to the width of a standard road, containing two 3.5m wide lanes, and also the same road, with 1m margins on each side. With a 7m width, the clearance from the bridge to the ground is 4.5m. With a 9m road width, the greatest road width that would physically fit within the bridge width, the clearance is 3m.
Figure 2: Bridge and platform
Figure 3: Photograph of the bridge
Figure 4: Scale drawing of the bridge and platform
The platforms are too close together
The standard width of a road lane is 3.5m. This allows traffic to comfortable use a lane, without the drivers feeling that they are being squeezed. Unguided buses tend to move apart from each other when they approach. The Orange Line, Los Angeles, shown, is 8.33m wide, and yet the buses still instinctively move apart. With the platforms set as they are, only 6.4m of road width is possible. Since buses are approximately 3m high, a road width of 7m would be possible, although this would require considerable alteration of the platforms.
The platforms are too high
According to the TfL manual for designing bus stops, a standard kerb height is 125mm, although a kerb height of 140mm leads to gradients when a boarding ramp is used. At most, kerb heights of 380mm are seen. The platform is apprimately 900mm above the rail level, and so standard buses could not be used without modification - undercutting the use of mass-produced buses. If the platforms are rebuilt, the costs would approach £2m. This would have to be done for every station along the rebuilt line. Larger stations would cost more to rebuild.
There isn't sufficient room for a properly designed road
To provide a proper road alignment, two lanes of 3.5m width would be required, together with a margin (so as to protect the bus from collisions with the bridge and other such items along the track). The required width is shown in Figure 5. Even a narrow road with two 3.65 lanes cannot be achieved in a width of less than 14.3m, which is wider than the bridge. The wide single carriageway, more suitable for buses (as was stated above), would require a width of 17m.
Figure 5: Standard Highway dimensions, rural mainline road (source: DMRB, volume 6, section 1, page 29)
An alternative approach is to use guided buses, removing the steel railway rails, and replacing them with concrete rails, therefore allowing the buses to run in as little as 6m of permanent way, just like a train. It is hard to see what the benefits would be, however, since the main advantage of buses over rail is their flexibility (being able to overtake other stationary vehicles and mixing express with stopping services). The cost of a guided bus system is also high, being of the order of £5m per km. And every single kilometre of track would have to be replaced. The worst outcome would be buses running on some part of a route, and, due to the need to keep intercity trains, running trains on other sections. At the junction between bus sections and train sections, passengers would have to change, which is only likely to ensure the decline in use of the services.
If a cheaper form of train is required, then there are many alternatives to conventional trains, including tram trains and rail buses.
At present, it may be simpler just to run bus and coach services to cover the last few stops of a commuter train which is travelling into a major city, for example London. As the commuter train moves towards the terminus, the number of passengers increases steadily, since many people are getting on, and few people are getting off. Eventually, the passengers end up crushed onto a train service for which they are paying large sums of money every year. It is difficult to increase the number of carriages, because train carriages are expensive, and at the other end of the line the trains run almost empty as it is. By providing bus and coach services linking the city to the nearest stops, the excess passengers can be carried in some comfort, and a lower cost, to their destination. Since this represents only a short service route, the lower speed of buses and coaches would not be a problem.
This proposal is shown in Figure 6. Buses and coaches would call at the railway stations for the last few stops, sharing the load with the trains when the trains are at their busiest. The service would stop on the road outside of the terminus railway station, with the bus stop marked as a platform, in keeping with the existing railway station. In the evening the system would work in the opposite direction.
Figure 6: Proposed bus relief system
