Tuesday, December 27, 2016

BRT and Congestion

The principle of equilibrium assignment suggests that it is unlikely that congestion will change much on the corridor. If BRT successfully reduces automobile congestion on the corridor, travel will be faster in that corridor, and Down’s ‘triple convergence’[1] from alternate routes, times and modes will occur. In that context, the amount of congestion experienced by automobile drivers on the BRT corridor is unlikely to change significantly. However, from a system user perspective, the BRT may provide substantial benefits by actually reducing the amount of diversion (and out of direction travel) that is currently occurring. If this is so, it would be reasonable to expect a drop in volumes along the diversion corridors. It seems likely that the combination of ITS features and dedicated transit guideway will serve to increase the overall capacity of the roadway, and that a drop in traffic volumes on the diversion corridors is a reasonable hypothesis.

However, if congestion increases, a ‘triple divergence’ to alternate routes, times, and modes will occur. How much diversion occurs will depend on how attractive the alternatives are. Assuming no significant addition in roadway capacity on alternate corridors, diversion to alternate routes will result in a slight worsening in overall congestion. Diversion to alternate times will make the ‘peak hour’ longer (AKA ‘peak spreading’). Diversion to other modes may or may not reduce 

Buses in general traffic lanes reduce capacity and increase congestion, a phenomenon well asserted both by the literature and by experience. The core principle of making transit ‘rapid’ is removing transit vehicles from general traffic lanes. This serves to both remove the effect of their operations on automobile traffic, and remove the effect of automobile congestion on transit vehicles.

As a thought experiment, assume the BRT is very attractive (in terms of time or cost), and attracts a large number of riders. This reduces automobile congestion along the alignment, making it faster. Drivers diverge from other modes and other routes, and the corridor becomes congested again. But only for automobiles--due to exclusive guideway, the BRT is less affected, and remains an attractive alternative. For drivers on the BRT corridor, there is no net benefit. For transportation system users, there are two classes of beneficiaries: BRT riders, and drivers on the diversion corridors.

A caveat to the benefits to drivers: The benefits to drivers on the alternate routes is going to get ‘lost in the noise’. They will be dispersed over a large number of roads, and reflected in small changes in the duration of peak periods, or in minor traffic volumes in a large number of roads. Provo-Orem is a rapidly growing metropolitan area, with substantial development taking place both north and south of the study area. Any minor advantage from the BRT to drivers will be rapidly eroded by additional land use changes.

A caveat to the benefits for riders: ‘rapid transit’ implies exclusive guideway; most BRT systems are only ‘semi-rapid’. While provided with transit signal priority, time separation (at intersections) provides a reasonable analogue to rapid transit conditions. However, the Provo-Orem BRT has only 51% exclusive guideway. Where the BRT lacks dedicated guideway, it will be exposed to the effects of congestion. In ideal circumstances, this guideway will be placed in the most effective location; where congestion is most intense. Congestion also tends to be greatest near intersections. Thus, roadways tend to be widest at intersections, where the road shoulder is used to provide turn lanes. Many worthwhile BRT projects have been subjected to the ‘death of a thousand cuts’; minor sacrifices made in the name of preserving automobile capacity (or worse:maintaining on-street parking).

However, given the number of routes that the also service parts of the BRT corridor[2], it is unlikely that all of the delay induced by local buses will be eliminated.

In the context, it seems likely that the corridor will stay at a very similar level of congestion. However,

[1] https://escholarship.org/uc/item/3sh9003x#page-4
[2] http://www.rideuta.com/-/media/Files/System-Maps/2016/Utah-County-System-Map.ashx

Friday, October 21, 2016

Rapid Transit In North America

Montreal Metro
Toronto Subway

Chicago L Train
RTA RapidTransit
Baltimore Metro
Boston 'T'
NYC Subway
Philly Subway
PATCO Speedline
San Fran's Muni-Metro

LA Metro

Wednesday, October 19, 2016

Transit Phases

Urban Transit in the United States has six major phases**:

  1. Street Railroads
  2. Subways/Elevated
  3. Street rail
  4. Bus-titution
  5. M/ART
  6. Light Rail
Street Railroads is exactly as advertised: Railroads reaching the city center, run on city streets. Noisy and dangerous, they are largely extinct. Most cities relocated several of them to a common corridor (typically as part of a Union Station effort). Building a 'viaduct' over them was a popular addition after WW2. Never electrified, they belched smoke and scalding steam as they traveled

Subways/Elevated were the first round of solutions to street railroads. Two solutions emerged: elevating them, and under-grounding them. As elevating is cheaper than excavating, it was the preferred alternative. (And railroads already knew how to build viaducts). Manhattan once had elevated rail-lines running down second and 9th avenue (of which the High line is the remainder). London forced another solution. The 'City of London', the original Roman square mile inside the greater metropolis of London has its own municipal government. Disliking the nuisance effects of railways, they simply banned them on city streets. (And now you know why London has so many railroad stations). But the value of bringing a rail-line INTO the center of London was simply too great, and so the Under-grounding began, in 1863. Chicago, with it's plethora of railways, still maintains its elevated stations ('The El').

Street rail: Everyplace with even a presumption of being a 'city' built a street railway. Using railroad track, these were smaller, lighter vehicles called 'trolleys'. There were a handful of attempts to draw them using engines, but electrification (using the pantograph) became endemic.* 

Inter-Urbans: A hybrid streetcar/railroad deserves a passing mention, if only for it's later importance for light rail. Combining street-running sections in urban centers, and railroad right of way between cities, they filled a niche market, typically by connecting urban destinations to entertainment or educational institutions. Some used trolleys, and some were special 'school trains'. 

Bus-stitution represents the dark age of urban transit. (To those who love trains, at least). Worn out trolleys were replaced were shiny new buses. (Cue Roger Rabbit). Streetcars were already in decline beforehand. The only rail routes to survive were underground/elevated systems, or places with awkwardly narrow tunnels. 

M/ART refers to the period between WW2 & the advent of light rail in the United States.  But in 1970, we recognized we had 'an urban transportation problem', which is the preferred euphemism for the explosive growth in traffic congestion.
Transit was the clear solution. But even the solution was a problem. Private companies had built most of the transit infrastructure before 1928, and municipalities getting into the game only in response to their failure. But no private entity was willing to build transit in 1970--competition from the automobile was just too fierce. Conservative pundits love to argue that this reflects the innate attractiveness of the automobile. They also love to ignore the billions of dollars in Federal subsidy provided for the Interstate Highway system. So, it order to compete with the automobile, transit projects required a subsidy. Given that the 70's were sort of the high-water mark of 'big government' and centralized planning, it became a Federal project.

None of them did terribly well, at least at first. They had very high costs per rider. For some of the systems, for some years, it would have been better to either a) buy everyone a cheap car, or b) put all of the money into buses. They've done better over time, as traffic congestion has worsened, and developers have responded to the accessibility premium of locations near them, so more things are near them. BART won its spurs when the Bay Bridge collapsed. The DC metro has become the most-ridden transit system in the US.

Light Rail The return of the inter-urban! Known as 'City-Rail' (Stadtbahn) in Germany, it made use of freight right of way, with street running portions in the center of cities. APTA called them 'light rail' so suburbs would accept them. Successful, at least judging by their popularity.  They make use of a variety of types of running-way.

Streetcars are history repeating itself. They are street-rail come again--trolleys operating in mixed traffic.  Portland has made them famous, and their use as a successful economic development project means that every major city in America is either building one, or planning to. The dividing line between street cars and light rail is not a clean one. (Salt Lake has a 'streetcar' in its own railroad corridor, and a 'light rail' on a city street'.)
Both make use of all types of running way. Streetcars generally have shorter lines, smaller vehicles, lower speeds, and more frequent stops. My analysis showed that average stop spacing is most distinctive. Portland, Tucson and the Tacoma Central Link all have an average stop spacing about half that for other systems. 

*Yes, cable-cars existed. Yes, a number of hilly places used them, most notably San Francisco. But even more places used funiculars, and I'm not mentioning them. Today, they are both simply exotic survivals. 

**BRT will require discussion elsewhere

**CRT too.