Advanced Buses

a description of what's available


This chapter describes some of the advanced bus technologies available. Advanced bus technology takes the following forms:

The purpose of buses

The World Bank did a study to investigate the future role of buses in urban transport. Figure 1 shows how buses, (labelled here 'BRT') occupy a niche of low cost development, with a substantial capacity. Figure 2 shows how buses make the most sense financially compared to other types of public transport, at least at lower passenger flows. At a certain passenger flow level, other forms of transport start to make more financial sense. By comparison, a typical urban bus service, running once every 10 minutes and carrying 50 people per bus would have a capacity of approximately 300 pphpd (passengers per hour per direction). This is why most urban public transport routes in the UK use buses.

Figure 1: The market sector occupied by bus services (Source: World Bank)

Figure 2: The costs of running bus services (Source: World Bank)

These considerations led to the use of buses in World Bank transport projects in Colombia. This video by the World Bank shows what they have done.

What's Wrong With Traditional Diesel Buses?

The major problem with diesel buses is pollution.

One of the ironies about buses is that they are seen as environmentally friendly, whereas cars are not. In fact, it is very much the other way around, as can be seen in Figure 3, where the relative emissions of cars and buses are shown. Because the emissions are shown per passenger, this graph takes into account the higher typical occupancy of a bus. Clearly, the emissions from buses are much greater than that from cars, made worse by the fact that a higher proportion of buses are old, than would be the case for cars.

Figure 3: Pollution from buses and cars (Source: Dr Parkhurst, UWE)

What's Wrong With All Buses?

The big problem for all buses, irrespective of engine technology, is safety. If a pedestrian is hit by a car, it is likely to be at a low speed, with the car driver having braked severely before impact, and the pedestrian may well survive the collision. The pedestrian is likely to end up going over the bonnet of the car. If a pedestrian is hit by a bus, by contrast, they are likely to go under the wheels of the vehicle, and be crushed by the weight (approximately 10 tons) of the vehicle. When a major construction project is undertaken, the local council can impose a Construction Management Plan on the developer, in which access routes for the heavy construction vehicles are agreed, which avoid residential areas. At the same time, the very same councils endeavour to route buses through residential areas. Either heavy vehicles impose a risk, or they do not, but both possibilities cannot both be simultaneously true.

This is a problem that trams have dealt with by fitting anti-crush guards to the wheels, so that pedestrians cannot go under the wheels. Is it possible to devise similar devices for buses?

Figure 4 shows the prominant warning message at the bus station in Bath, UK - "Pedestrians - Extreme Danger - Enter Bus Station Via Passenger Entrance". This is quite a contrast to a supermarket car park, where pedestrians can approach the parked vehicles from any direction. It demonstrates that buses are not as safe as they are usually made out to be.

Figure 4: Warning message at Bath bus station, UK

Diesel-Electric Hybrid Buses

A diesel-electric hybrid bus is shown in Figure 5. The bus drive-train works in a similar way to a Toyota Prius. A diesel engine charges the batteries. The batteries drive the electric motors located in each drive wheel. The advantage of this system over a traditional bus is that the diesel engine is never placed under strain, and it can run at its most efficient setting. This reduces emissions quite dramatically, as shown in Figure7. (Source: Federal Transit Agency).

Figure 5: How a diesel electric bus works

Figure 6: Diesel-electric hybrid bus (Source: London Bus)

Tfl London is claiming even higher reductions in emissions, based on their testing. The main advantages of the diesel-electric bus are that it uses the same diesel fuel as any other bus, they are driven in the same way as a diesel bus, and therefore can be accomodated in the service schedule like any other bus. Figure 8 shows the fuel consumption of diesel-electric buses, and Figures 9 and 10 show their running costs. Note the major cost of replacing the batteries on the diesel-electric hybrid buses. (Source: Federal Transit Agency).

As can be seen, the main disadvantage of the diesel-electric hybrid bus is the cost of buying the buses (about 50% more than conventional diesel buses), and replacing the batteries,which exceeds the fuel savings by a large amount. In the USA, the extra cost is about 1.3 cents per seat mile, whereas the fuel for an ULSD bus is 0.23 cents per seat mile more expensive. This doesn't sound like much, but over many years, a large bus fleet, and many miles, the difference can be millions of dollars.

The situation may be different in the UK. The cost of fuel is approximately $10 per gallon in the UK, but only $2 per gallon in the USA. Therefore, it may well be that the savings in fuel outweigh the costs of the vehicles and batteries. Certainly, in a regulated bus market, where costs are less important, the reduced emissions of the diesel-electric hybrid bus may be worth the extra cost. The only regulated bus market in the UK, London, is planning to take delivery of a large number of these vehicles by the time of the Olympic Games in 2012.

Fuel-Cell Buses

Fuel-cell powered buses work in a similar way to a diesel-electric hybrid bus. The fuel cell turns hydrogen (from a fuel tank on the roof) and oxygen from the air into water, producing electricity. The electricity is fed into batteries, and the batteries power the electric motors in the drive wheels. It is possible to link the fuel cells directly into the drive wheels, but then the fuel cell would have to produce more peak power, which would make the bus more expensive. This process is shown in Figure 11.

Figure 11: How a fuel cell bus works

Figure 12: Fuel cell bus (Source: London Bus)

Fuel cell buses are very expensive, although they may drop in price in the future - the cost, as of February 2006, is 1.5m each, equivalent to 20 conventional diesel buses. TfL, London, is the only transport organisation in the UK with fuel cell buses, although they only have a few of them on trials.


The trolleybus works in a similar way to a tram, although the trolleybus has two overhead wires instead of one. Current flows along one overhead wire, down the pickup arms, through the motor in the drive wheel, and then back into the other overhead wire. This process is shown in Figure 12.

Figure 13: How a trolleybus works

The main advantages of a trolleybus are that the bus is quiet, vibration-free, with no pollution in the street. The main disadvantage of a trolleybus is the bus needs to be wired up, at a cost of 1m per kilometre. This may appear to be expensive, but the equivalent tram system would cost 20-30m per kilometre. Despite this, in a deregulated bus market it would be difficult for a private bus company to justify this expenditure, and they run the risk of being undercut by another bus company which didn't make the investment. Trolleybuses are also more expensive than a traditional diesel bus. Only in a franchised market are we likely to see trolleybuses.

Britain has had trolleybuses before. The problem was that the bus pickup arms came away from the overhead wires too easily, particularly on corners. When this happened, the bus would stop, having run out of power; and also, the overhead pickup arms could get entangled in the wires, causing damage. The driver would have to get out of their cab in busy traffic, and use a pole to try to reconnect the pickups to the wire. Diesel buses were easier to handle.

Modern trolleybus wiring is better designed, making it harder for the pickups to disengage. Modern trolleybuses often have an auxillary power supply to move the bus if the bus loses electrical power. Modern trolleybuses also have a winding mechanism which stops the pickup arms from popping up too far, and which enables the pickups to be repositioned from inside the cab.

The wiring on a trolleybus can produce visual blight. On a simple wiring run, the cabling is not obvious (Figure 14), but in the case of a junction, with wiring intersections called 'frogs', the dense wiring pattern can be intrusive (Figure 15).

More information on trolleybuses can be found on the internet, particularly the Trolleybus UK website. There is also another website for Leeds.

Figure 14: Trolleybus, Massachusetts - WM/Arnold Reinhard Figure 15: Trolleybus wiring at a junction - WM/Fred Hsu

YouTube has some videos of Trolleybuses, particularly this one of Trolleybuses in Rome.

A trolleybus in full flight is a thing of beauty, indeed.

The obvious question is this - why aren't there more trolleybuses around?

Transport for London's response was as follows:

Regrettably, trolley buses are no longer generally considered to be a viable solution for London's transport needs. Whilst they may offer some marginal energy efficiencies compared with 'conventional buses' these are likely to be more than offset in pure cost terms by the cost of supplying and maintaining the electrical power supply infrastructure.

Ongoing developments in bus technology, such as the hydrogen fuel cell buses and hybrid diesel-electric buses which have been on trial in London can deliver many of the environmental benefits of the trolley bus without the need for the fixed infrastructure. The combination of these factors makes the consideration of trolley buses low on TfL's current plans for investment in the network.

As far as I am aware, none of the infrastructure for former trolley bus services remains today. In many cases, trolley buses would have been directly replaced by normal buses. However, since then, the London bus network has expanded significantly, and routes are under continual review. Consequently, it is not now possible to say which bus services were direct replacements for trolley buses.

Articulated Buses and Double-Decked Buses

As long as the seats can be filled, increasing the size of the bus means that more passengers can be carried per driver. All bus companies have a major problem filling vacancies for bus driving, as the hours are long, and the job is not particularly well paid. Buses can be increased in two ways - vertically and horizontally.

Increasing the size of the bus vertically means adding another deck to the bus, creating the double-decked bus. This has the advantage that the bus length is not increased (and so the turning circle isn't increased), but on many routes there is a height limitation, due to low bridges. Bath, UK, along with many UK cities, has a railway line running through it, and this imposes severe height restrictions.

The alternative approach is to length the bus. In order to reduce the effective length of the bus, and to prevent the bus becoming so long that it becomes unwieldy, the bus is split into two pieces, with a connector underneath the floor of the bus. Even so, the turning circle is increased. Generally, an articulated bus only has two segments in it, since the two-segment bus is already long enough and unwieldy enough. It is possible, however to have buses which are bi-articulated, that is to say, with three segments and two connectors.

Typical vehicle dimensions and turning circles are shown in Figure 16.
Figure 16: Typical bus dimensions and turning circles (Source: AutoTrack)

In traffic congestion terms, the double-decked bus takes up no more road space than a single-decked bus, and therefore the crucial measure of congestion caused per passenger is reduced. The articulated bus takes up more space on the road than a traditional bus, but the increased number of passengers mean that the congestion caused per passenger is reduced further. Typical values shown in Table 1.

Table 1: Congestion per passenger

Figure 17: Articulated bus, Hamburg, Germany - WM/KMJ Figure 18: Double-decker bus, Tokyo, Japan - WM/Comyu

Bus Rapid Transit

Bus Rapid Transit is buses on steroids. The flow of passengers along a route is determined by the interval between buses, and the capacity of each bus. Since the size of the bus is largely fixed, the best way of increasing the number of passengers that can moved is to increase the frequency of the buses. Increasing the frequency of the buses involves removing some of the restrictions on the number of buses than can be run per hour. The problems and the solutions are detailed in Table 2.

Table 2: Bus Rapid Transit Strategies

A typical bus stop layout is shown in Figure 19 and Figure 20. The bus lane has widened out to two lanes, allowing the red local stopping bus to park alongside the bus stop, whilst the white express bus continues at full speed along the route. The ability to mix stopping and express services is unique to bus rapid transit - most trams are laid as one track in each direction. A smaller bus stop layout is shown in Figure 21, which shows a bus stop in Curitiba. The extending ramps, built into the bus stop, which connect between the bus and the bus stop are clearly visible. Figure 22 shows a bus stop on the Transmilenio line, although it doesn't show the turnstiles provided for pre-payment customer access.

Figure 19: Typical BRT bus stop layout Figure 20: Photograph of Transmillenio system (Source: Transmilenio)
Figure 21: Bus stop in Curitiba (Source: FTA) Figure 22: Transmillenio system bus stop (Source: Transmilenio)

The capacity of BRT systems can be very high. Mexico City's system can move 9000 passenger per hour, whereas the larger Transmillenio system in Bogota, Colombia, can carry 1.3 million passengers per weekday.

Demand Responsive Transit

Demand Reponsive Transit or DRT differs from conventional bus services in that the routes are more flexible. The bus can detour from the scheduled route a bit, in order to pick up passengers outside their homes, and drop them back off again. It is typically used in rural communities, in place of a conventional bus service which may not go past enough houses to provide a good service.

Typically, the service is provided by a minibus. The bus company run a hotline, and the passengers ring up the hotline when they want a bus to arrive.

The drtbus website provided a very good guide to what DRT can provide. One of the case studies is for Genoa, where narrow streets meant that a conventional bus service would have been inappropriate. Arguably the most famous DRT service in the UK is the Wigglybus in Wiltshire, now renamed Connect2Wiltshire.

Guided Buses

A guided bus is a normal bus, running on special track, and with additional guide wheels at the front of the bus in order to keep the bus running straight down the track. Because the bus is guided along the track, the width of the route that the bus needs is reduced, and so the bus can fit into much narrower lane widths than would otherwise be the case. This is particularly true where two buses approach one another, where without guidance the bus drivers will tend to steer apart, increasing the lane width required - this is shown in Figure 23 (source: Light Rail Now.)

Figure 23: Photograph showing buses moving aparts as they pass - Orange Line, Los Angeles

Figure 24 shows the guided wheel system on guided bus (with the front of the bus to the left). These additional wheels make contact with the edge of the trackway, and hold the position of the bus, as shown in Figure 25. Because the guided bus is in all other respects a normal bus, it can be driven around the local streets at the end of the guided bus track.

Figure 24: The guide wheel mechanism on a guided bus - WM/Martin Hawlisch

Figure 25: How the guided bus mechanism works

The track is typically made from concrete sections. Figure 26, showing the O-Bahn guided bus service in Adelaide, Australia, shows the cross-section of the track. As shown, a space is usually provided between the running area, in order to stop cars being driven along the track. What is possible with guided bus is shown in the initial design for the Emerald Express system, Eugene, Oregon, in Figure 27, where the track has been landscaped in order to improve the streetscape. The fact that the guided bus only runs along narrow tracks, with the gap between untouched, allows the area in-between to be laid to grass.

Figure 26: O-Bahn, Adelaide, Australia - WM

Figure 27: Initial designs for Emerald Express, Eugene, Oregon (Source: Newlands & Co. {})

Video footage from Youtube shows how the system works in practice -