There are four basic transit guideway types, as shown in the above graphic:
- Elevated Reserved
- In‐Street Non‐Reserved
- In‐Street Reserved
- Tunnel Reserved
Tunnel reserved right‐of‐way meets these criteria and can offer significant mobility benefits beyond those of other guideway types. However, the extremely high cost for such exclusivity makes this option nearly prohibitive to deploy in most cases.
To a lesser degree, elevated reserved guideway provides many of the same mobility benefits, but is subject to physical obstructions, like buildings and trees, and
the weather, and is still very expensive.
The costs for grade‐separated, reserved guideway are about two‐ to three‐times more expensive for elevated than surface transit. Tunnels are typically two‐ to three‐times more expensive than are elevated. Both grade‐separated options would encounter major design hurdles along the recommended alignment at the two crossings of I‐35, where the multi‐level highway presents physical obstructions that would likely require costly work‐arounds. Tunnel guideway would have to contend with crossing under both the depressed Dean Keeton Street at I‐35 and the depressed I‐35 main lanes at East Riverside Street, along with Lady Bird Lake.
On the other hand, elevated guideway would have to go over the current aerial section of I‐35 at Dean Keeton Street. Elevated guideway would also present a considerable visual obstruction and may not even be attainable within Capitol View Corridors. At‐grade guideways, both reserved and non‐reserved, offer much lower costs and improved access (no stairs, escalators, or elevators) over grade‐separated types. While reserved right‐of‐way can offer better reliability, options for obtaining it within the identified corridor exist only excess right‐of‐way exists or where parking can reasonably be removed.
Acquiring entirely new right‐of‐way corridors, or expanding existing ones within Central Austin, would be prohibitively expensive in terms of property costs, legal proceedings, and social costs associated with the necessary displacements. However, where reserved right‐of‐way is available within the study area (along East Riverside Street and around ABIA property), it is recommended that the proposed vehicle be able to take advantage of it.
Another hybrid guideway type is semi‐exclusive, or semi‐reserved, in which the guideway takes the form of a designated travel lane without a physical barrier or separation. Semi‐exclusive guideway offers reliability benefits because the transit service is in its 'own' lane and is less disruptive to the right‐of‐way since it fits within it. But, semi‐exclusive reduces the auto capacity of the roadway, which may not be desirable along some segments. Therefore, in‐street non‐reserved guideway is the most appropriate option for Central Austin because it is least expensive and least disruptive.
Austin Transportation Department presented their Urban Rail Alternatives Evaluation to the Austin City Council. This is the first phase of an ongoing planning effort to explore Austin's options for a rail system serving key urban destinations and adding connections to the regional transit and mobility network. All week we will be exploring and want to hear your thoughts about this study. Be heard!