Track facts – Modern light-rail track

The recently built tramtrain line in Heilbron Germany

There has been much debate about the cost of track laying and the cost for new tracks for light rail or streetcars. The following will hopefully shed some light on how modern LRT (streetcar) tracks are laid on-street. With the interurban, of course, the majority of the route will be shared with other railways and the costs would be to upgrade existing tracks (relaying) and adjustments to switches. Portland Ore. give good insight on modern track laying principles.

The Portland streetcar is laid with girder rail, set in concrete, which is sturdy enough to handle the larger MAX LRV’s. The main problem is that the streetcar line has tighter turning radius, which the larger LRV’s can’t negotiate.

The continuedAi??Ai??nonsense about relocating utilities has more to do renewing utilities on the back of light rail construction, and making work for municipal employees than anything else.

Many alignments of new LRT systems are increasingly placed in public thoroughfare rights-of-way (on-street). For example:

Ai??Ai?? Portland A?ai??i??ai??? over 28%
Ai??Ai?? Sacramento A?ai??i??ai??? nearly 23%
Ai??Ai?? San Jose A?ai??i??ai??? nearly 56%
Ai??Ai?? Dallas A?ai??i??ai??? over 20%
Ai??Ai?? Salt Lake City A?ai??i??ai??? nearly 19%
Ai??Ai?? Tacoma A?ai??i??ai??? 100%
Ai??Ai?? Houston A?ai??i??ai??? 100%
Ai??Ai?? Minneapolis A?ai??i??ai??? nearly 22%
Ai??Ai?? Phoenix (planned) A?ai??i??ai??? over 95%
Ai??Ai?? Seattle (planned) A?ai??i??ai??? over 32%

As much as possible, construction methods and practices which have significant potential for lowering costs should be considered. For example, in the case of the Portland Streetcar, the shallow-slab construction method (see Figure 3) proved to be a major cost-saving technique for in-street construction. Instead of digging three and four feet deep, disrupting utilities, and rebuilding much of the street in the process, builders use a quick “cut and cover” European-style track system that goes down between 12 and 18 inches and is 6 to 7 feet wide. A pad is laid down, followed by a light layer of gravel, and then a special dual rebar side frame is laid into this shallow trench.

Each running rail is encased in a “rubber extrusion rail boot” to provide electrical isolation as a corrosion control measure. This covers the rail entirely wherever there is ground contact, and is then attached to the specially shaped rebar frame with dielectric fasteners. The boot also provides some basic level of noise/vibration attenuation. The boot-encased rails are held only by the concrete between anchor plate assemblies, which are placed at 3.0-meter intervals on straight track and broad curves, or at 1.5-meter intervals on curves sharper than 300 meters in radius. The fastener assemblies remain separated from the running rails by the rubber boots to maintain electrical isolation of the rails. There are no gauge bars.

A major advantage is the minimization of subsurface utilities relocation. Instead, a kind of “bridge” (the slab, carrying the guidance rails) is installed over utilities. This enables utilities workers to make an adjacent excavation, as necessary, to access under-street utilities for repairs or other servicing.

Slab depths are 300 mm (about 12 in) for the RI 52 girder rail used on streetcar construction for cars weighing about 30 tons empty, and 360 mm (14 inches) for RI 59 girder rail used where streetcar and “interurban” tracks cross. Prudent planning would suggest designing and building for future use of heavier, interurban-type vehicles, since these might ultimately be needed if the original system is successful. It’s far more difficult to upgrade under-designed trackage than to upgrade stations and procure larger vehicles. To accommodate the possibility of heavier, “interurban”-style LRT in the future, a slab depth of 18 inchesAi??Ai??is sufficient. If the design of the rail line is to be in a raised median, then a depth of 12 inches can be maintained, with the slab, rising in a media, six inches above the roadway.

Seems a whole lot simpler and cheaper than tearing up entire streets and moving utilities, but then, this is exactly what the SkyTrain lobby wants!