I have an old friend who works on the catenary who has suggested otherwise, and based on the engineers I've talked to this is not the case - speed limit is much lower than that, the poles being closer together is inherent to the design.
Using different contact in tunnels is common, I haven't looked at it in the tunnel in quite some time, but I assumed it was semi-rigid (which of course still has a "wire") which is common around the world. Lower speeds are usually ok in a city centre tunnel with fairly tight spacings, and mounting is typically much more rigid.
The OCS definitely supports lower speeds without a support wire, the frequency of poles does not mitigate for that. Single wire design is common for
low speed trams and depots, without a support wire you are going to have lower allowable speeds - "At the other end of the scale, a tram depot may have just a single wire hung directly from insulated supports. As a pantograph passes along it, the wire can be seen to rise and fall." - the amount of tensioning possible through the supports is limited (it tends to largely come from the panto). Some good reading for those interested here:
http://www.railway-technical.com/infrastructure/electric-traction-power.html (Piers Connor is great)
Sorry late reply. I had to do some research into this one.
Firstly, your links. I was REALLY hoping they would have some specifics, such as X type construction allows operation of LRV's at X speed, while Y type of construction allows operation at Y speed. Unfortunately, that was not the case. In fact, trying to find any information like that is very tough. I've ended up reading though a number design guidelines for LRT lines, which off the top of my head included: San Diego, Denver, Metrolinx, Phoenix, as well as few documents from the Transportation Research Board. A number of documents did differentiate between simple contact wire, and a tensioned, flexible contact wire and simple catenary.
I did double check today. In particular, the tunnel from South Portal to University Station has a speed limit of 70 km/h. It features elastic support arms, which ETS's design standards call for 11m spacing. It is a single, tensioned contact wire. It is NOT catenary, so most certainly with proper design a single contact wire does support 70 km/h speeds on Edmonton's LRT. I believe North Portal to Grandin might also be 70 km/h, but there is also a section break right North Portal so trains do have to coast through that.
This is where my assumption comes in: the Blatchford extension in an attempt to make a more esthetically pleasing OCS, it uses a flexible, tensioned single contact wire. On account of not having the messenger cable, the span length between poles is reduced to compensate, but should surely have no problem supporting higher speed operation if the track allowed it. Just because ETS chose this OCS design it is not sign that Edmonton is trying to lower the speeds to an "urban LRT".
Incidentally, the Valley Line has a 65 km/h zone in the Quarters tunnel, again with flexible suspension of a single contact wire.
I did find two sources to support my assumption that the design of the Blatchford extension catenary is not necessarily limited to slower speeds.
Page 65:
"The flexibility and performance of the OCS can be improved by providing the contact wire with a flexible support in the form of a bridle. This is more commonly used in LRT systems where speeds can operate to 80 km/h. The contact wire may either have fixed terminations or be automatically tensioned. Parallel feeder requirements are similar to the simply suspended OCS."
This one is actually an Edmonton source, Robert Clark:
https://www.trolleycoalition.org/pdf/lrtreport.pdf
Page 63:
"The simplest design of overhead conductor has proved sufficient in most cases for speeds up to 50 km/hr. This was designed originally for trolley poles and uses a single conductor with more or less flexible supports at 30 m (100 ft.) intervals; both ends are anchored. Temperature change leads to a change in the sag of the conductor which must be compensated for by vertical travel of the pantograph. A system which incorporates automatic tensioning guarantees a constant sag and may be used for pantograph operation at speeds of up to 70 km/hr. Earlier installations used a weight and pulley system to achieve this tensioning similar to the catenary system, but modern design achieves constant sag through support of the conductor by angular disposition of drop wires. The overhead is erected in zig‐zag fashion between from support to support and expansion due to temperature change is accommodated by change in the angle of the hangers. This is the type of suspension which is currently in use on trolley bus routes in Edmonton (Figure 9.15.1). It is the cheapest to construct and maintain and would be suitable for application to rights‐of‐way in categories C, D, and E when speeds are not likely to exceed 70 km/hr. because of constraints other than overhead design, and power demand is moderate."
I was quite curious myself if there were posted speed limits along the Blatchford extension beyond the NAIT station. There are not, other than some 30 km/h signs for approaching the station. However, there is a sign declaring that you are leaving ABS authority, and entering yard limits, so presumably that's why there' are no posted speed limits because yard rules apply. Naturally, this will change once the track to the Blatchford Gate Station open, but, until then... yard rules and speeds.
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