Thursday, August 4, 2016

Yesterday's Truck Crash should Remind us of Flex Lanes

Yesterday's truck crash on one of the bridge off-ramps will doubtless provide fodder for those who believe we need a new bridge.

Note now little traffic is on the Marion St. Bridge (top)
that's wasted capacity!
(Devin Fadenrecht / Special to the Statesman Journal)

But delay may not have been all that significant. Not worth $1 billion, anyway.

The paper described it as backing up for "nearly three miles and causing congestion for more than six hours." But how much slowing and delay actually occurred? Significantly, not all traffic was backed up: Bike traffic was much less affected, it should be noted.

Aerial from 2014 crash-induced traffic backup
It has always seemed like there ought to be contingency plans for temporary two-way functioning of the bridges, especially to use the surplus lane capacity in the "reverse commute" direction. (Other examples from 2014 and 2015.) When the Center Street bridge is slow, why are we not able to use some of the Marion Street Bridge? That is a huge amount of wasted capacity, and doesn't require any new lanes be built.

Center St Bridge Seismic Preapp Sheet
Since it looks increasingly probable that we will have a seismic study for the Center Street Bridge, and that the reinforcement will make sense in a catastrophe only if two-way traffic is accommodated on the Center Street Bridge, there may be a formal entry to look more at contra-flow lanes, temporary or permanent.

And in fact, one of the discarded options would have formalized permanently two-way traffic. It was rejected because it "would require a major re‐engineering of the existing street system" and this was seen as too disruptive and, consequently, too expensive.

But it's hard not to wonder if it deserves a second look and more serious consideration, or if parts of it could be retrieved for a lower-tech and non-permanent approach to rush-hour congestion or crash congestion. Flex lanes may not have been considered sufficiently.

At this point this may be only of academic interest, unfortunately, but maybe there would be new interest in it. (I had been searching for "brown" for a couple of years now and kept coming up null. But it is actually in the DEIS under a different name, which I missed!)

For convenience, here it is from Chapter 2 of the DEIS.

The Brown Alternative
Two 2-Way Bridges Alternative
The intent of the Two 2‐Way Bridges Alternative was to make the existing Center Street and Marion Street Bridges into two‐way facilities. With this alternative, one bridge would be for local traffic and the other bridge would be for regional or through traffic. Theoretically, this would improve traffic flow by reducing the conflicts and merges among the two traffic streams.

Reason for Dismissal
Technically impracticable (bridge connections and street grid system). From a traffic flow perspective, the benefits of separating local from through traffic are well known. The typical application is a facility, such as an expressway or freeway. By definition, access to such facilities is controlled and limited. As more traffic flows or movements intersect the facility, more separate structures (for example, lanes and ramps) are needed to achieve the flow (operations) benefits desired.

The Center Street and Marion Street Bridges are integrated into the surface‐street system in a grid fashion. To separate regional from local flows would require facilities on both sides of the Willamette River that would direct all local flows to and from one bridge and all regional flows to and from the other bridge. However, downtown Salem and West Salem are each key destinations for both local and regional traffic. Therefore, to provide the desired mobility, each facility would need to provide all movements (that is, regional‐to-local, regional‐to‐regional, local‐to‐regional, and local‐to‐local). Multiple connections would be needed between each bridge and the major north‐south surface streets (primarily Liberty and Commercial Streets on the east side and Wallace Road on the west side). In addition to providing all the connections, the facilities would need to be separated enough physically to avoid conflicts that would result in congestion. Without this physical separation, the envisioned benefits would not be achieved because congestion on the surface‐street system would continue or worsen.

While two‐way bridges would address one part of the Purpose and Need (mobility across the Willamette River), they would not alleviate congestion on the connecting street systems, in particular at the key intersections at the bridgeheads. Successfully directing the two different traffic flows (local vs. regional/through) to the two separate bridges would require a series of intersections and ramps among the two bridges and the major north‐south routes. Doing so, however, would require a major re‐engineering of the existing street system. For example, ramps and new connections would have to be constructed that would extend well beyond the current bridgeheads (perhaps one to two blocks in multiple directions). This connect with and improve. For these reasons, the Project Management Team concluded that the Two 2‐Way Bridges Alternative was not a technically feasible solution for this project.

Other Considerations
  • For this project, the limiting factor with respect to vehicle mobility across the Willamette River is not the capacity of the bridges themselves. Rather, the limiting factor is the ability to accommodate multiple traffic movements at each end of the bridges. As described previously, to integrate all movements from the two 2‐way bridges into the surface‐street system would require ramps and new connections that would extend well beyond the current bridgeheads (for example, one to two blocks in multiple directions). Providing this infrastructure would require the removal of several blocks of buildings in the core commercial areas of both downtown Salem (east side of the river) and West Salem (west side of the river). Preserving and enhancing the viability of these two commercial areas are goals of the project. These goals are consistent with several key policy statements from the Salem Area Comprehensive Plan (City of Salem, 2009a). In comparison, the other alternatives being considered would have few or no such impacts on these locations.
  • The Two 2‐Way Bridges Alternative would cost roughly twice as much as just widening the existing bridges ($500 to $600 million vs. $250 to $300 million). However, this alternative would not provide the transportation performance benefits (degree of mobility) associated with the other alternatives in this higher cost range. Constructing an alternative like this with the desired mobility benefits would impact business and commercial areas as described previously. Other alternatives being studied in the DEIS would provide similar functions in the same crossing location but at less cost and/or with substantially less impact on the neighborhoods at each end of the bridge.
The Purple Alternative and Land Use Laws

Another interesting discarded option is the "purple" one. It is interesting because of the discussion of the UGB. On a superficial reading, an analogy seems possible:

Purple:Salem Alternative::Salem Alternative:2A

The same criticism of the Purple alternative relative to the Salem Alternative can be made of the Salem Alternative relative to widening the existing bridges. Maybe this is also a partial model for criticizing the proposed UGB expansion and Goal Exceptions.

Reason for Dismissal
Environmentally impracticable (impact to protected agricultural lands).
The Purple Alternative would have substantially greater impacts than other alternatives on EFU lands that are protected by state land use laws outside the UGB (640 acres vs. 130 or fewer acres for other alternatives; see Table 2.2‐2). The impacts would include bisecting farmland and converting approximately 640 acres of farmland into transportation uses. Because other alternatives would meet the transportation need without an exception to Statewide Planning Goal 3, Agricultural Lands, or with substantially fewer impacts to farmlands, the Purple Alternative would not meet the criteria for a goal exception pursuant to Oregon Administrative Rules (OAR) 660‐012‐0070. The legal standard requires that a goal exception would not be granted if there are reasonable alternatives that do not require an exception (OAR 660‐012‐0070 [5]). Where there is a project and there is an alternative that does not require a Goal 3 exception, then all alternatives that would require a Goal 3 exception can likely be eliminated from further evaluation. If all the alternatives would require an exception to Goal 3, then the net impacts (with mitigation) of the preferred alternative “cannot be significantly more adverse than other alternatives also requiring an exception” (OAR 660‐012‐0070[7][a]). Although this determination considers the balancing of many environmental factors, in this case, the amount of agricultural land the Purple Alternative impact would be approximately five times greater than with the other alternatives. Furthermore, the Purple Alternative would bisect a large, currently farmed area, but the other alternatives would not. Instead, the other areas would impact land that is outside, but immediately adjacent to, the UGB.

1 comment:

d. davis said...

Anecdotally, witnesses on the bridge said some of the traffic slowdown was caused by driver behavior: Drivers originally wanting to exit to southbound Front decided to cross three lanes to the northbound Front exit rather than continue to Commercial. Sort of a head-scratcher.