After my recent post on the CBD and South East Light Rail (CSELR) the final $2.1 billion cost was revealed with the signing of the contract for the project in December last year. The half-billion dollar increase from the government’s previous estimate of $1.6 billion took a lot of people by surprise and contributed to an interesting and protracted debate in the Transport Sydney blog about whether light rail is the most appropriate and cost-effective mode for that corridor. The government’s announcement also revealed more about the technology to be used in the wire-free section of George Street.

I’ll discuss the cost issue in a future post, but in the meantime I thought I would investigate further the choice of Alstom’s “Aesthetic Power Supply” (APS) over battery technology to power the wire-free section of the line in George Street. As I outlined in my previous post, this system involves a continuous electrical feeder “third rail” embedded in the road surface between the tracks. This arrangement is claimed to be safe for pedestrians as it comprises conducting segments placed at regular intervals separated by insulated joints which are energised as the light rail vehicle (LRV) passes directly over them. Power is collected through two collector shoes under the LRV.

Diagram of the APS power supply (source: Systra 2012)

The choice of this system has already attracted some criticism both on cost and reliability grounds. I decided to look at both these issues, especially the aspect of reliability given Sydney’s recent summer torrential rains. I came across an interesting report prepared by Systra in relation to the extension of Dublin’s LUAS light rail network which assessed the wire-free power alternatives, including the Alstom APS system. I posted several replies on the Transport Sydney blog stemming from that report but I thought I’d consolidate them into a single post here.

The report includes a number of relevant comments regarding the APS system which are worth quoting in detail:

Specific features

The maximum operating speed on APS sections is 50 km/h, while an Alstom Citadis vehicle can operate at 70 km/h with overhead catenary…. In order to mitigate local failure of the system, the vehicles are equipped with batteries. These batteries enable trams to cross failed sections of up to 50 meters. (P11)

Mechanical aspects

The APS solution requires the installation of a power rail between the running rails, embedded in the track bed… In the BXD context, the power rail must be able to withstand continuous road traffic for years, without damage.

On French projects, APS is mainly installed on segregated running sections, except for road intersections where road traffic crosses the rail… As part of its certification process, the first version of the APS system went through an endurance test to simulate the effect of urban traffic (over 700,000 cycles with 7-ton pressure wheels).

Despite this test and certification process, the first version of APS installed in Bordeaux in 2003 suffered damage at road intersections. It is worth mentioning that in this previous design, the APS rail was directly embedded in asphalt… Following this experience, Alstom revised its design to embed the APS rail in a concrete plinth to increase its resistance to road traffic. This improvement ended up being satisfactory in Bordeaux.

The latest design of APS (APS 2) now includes a reinforced power rail, still embedded in a concrete plinth. Alstom claims that it can withstand 13.5 ton axle loads.”(P18-19)

Flooding

The APS power rail, like any power rail, cannot operate when it is covered by water, because such a situation would lead to current leak when the rail is powered up, and thus tripping of the circuit breaker protecting the traction power circuit…. Flooding of the track bed is an exceptional situation which should be prevented by an appropriate drainage arrangement embedded in the track. (P20)

Energy efficiency

For safety reasons, regenerative breaking is not possible when running with the APS system, thus energy efficiency is degraded by 15% to 20%…. The cost associated with this increase in the power consumption is difficult to estimate accurately at this stage. In order to carry out this estimate, many assumptions must be made; each of them introduces potential uncertainty in the result. (P22)

The report also makes some observations about the cost of the system:

Alstom APS

The APS system is made of on-board equipment and track side equipment. To this date, on-board equipment has always been delivered on new trams…. The cost of this on-board equipment delivered on a new tram is estimated to be around 300,000 €, in addition to the basic cost of the tram.

… The cost of the APS track side equipment is estimated to be 1,850,000 €/km. (p33-34)

It is always difficult to extrapolate estimated costs from one transport project to another in a completely different city 12,000 km away, but the report’s estimate provides a starting point. Assuming 25 LRVs for Sydney, the installation of one kilometre of wire-free track and allowing for inflation since the Dublin report was published in 2012, the total additional capital cost of the wire-free option for Sydney would appear to be in the ballpark of $15,000,000. This doesn’t include any saving from overhead wiring not installed in this section, but it also doesn’t cover any additional costs that may be involved in providing extra drainage to protect the APS conduit from the impact of flash flooding.

While this isn’t exactly cheap, it appears that adopting the APS system won’t make a huge contribution to the substantial cost increase announced for the CSELR. On the other hand, the criticism that the APS will increase the cost of electricity by 20% does appear to be borne out by the Dublin report, albeit with considerable qualification. This would apply however only in the wire-free section which will make up only around 10% of the CESLR track length. This means that the overall impact on energy use is likely to be relatively minor.

The more substantial concern raised in the media (which I discussed in my last post) is that use of any wire-free technology tends to lock a light rail system into using only the rolling stock supplied by the system’s manufacturer, in this case Alstom. The Dublin report also suggests that there may still be some serious questions over the reliability of the system in torrential rain and, possibly, in relation to the potential for damage at intersections.

I’ll return to the wider issues of the cost and appropriateness of the CSELR in a future post.