Reversible

On November 5, 2014 · 3 Comments

It dawned on me recently, as I drove around the Washington, DC area, that there seemed to be an inordinate number of reversible road lanes that switched directions on regular schedules. The occurrence that got me thinking about this was a one-block section of Washington Boulevard (map) on the western edge of Arlington’s Clarendon neighborhood


Reversible Road Lane
Washington Blvd., Arlington, Virginia, USA
via Google Street View, July 2014

I’ve driven through that slot a number of times and I never gave it much of a second thought. It seemed rather self-explanatory. Overhead lights with green arrows and red x’s denoted lanes that could be traversed depending on prevailing morning or evening traffic patterns. It made sense even if it lasted for such a short distance. It was the only three lane segment with four lanes radiating from either end. It saved on construction costs.

The variety of different types of reversible lanes also surprised me as I started ticking-off some nearby examples.


Overhead Lights


Stupid Young Driver on Cell Phone in Closed Lane on Chesapeake Bay Bridge!
Stupid Young Driver on Cell Phone in Closed Lane on Chesapeake Bay Bridge! by William Johns, on Flickr
Creative Commons Attribution 2.0 Generic (CC BY 2.0)

The Chesapeake Bay Bridge (map) connecting Maryland’s eastern shore to the rest of the state provided yet another example of overhead lights signaling traffic flow. The bridge accommodated prevailing traffic to and from Atlantic Ocean resorts especially during the summertime. More lanes opened towards the beach on Fridays and pointed back towards home on Sundays, almost like the ebb and flow of tides.

Overhead lights exposed an inherit problem: people needed to understand that lanes could reverse and they also needed to know what the symbols meant. "Stupid Young Driver on Cell Phone" had obvious difficulties with one or both of those concepts.


Just a Sign


'Signs' -- Chain Bridge (VA) January 2014
'Signs' — Chain Bridge (VA) January 2014 by Ron Cogswell, on Flickr
Creative Commons Attribution 2.0 Generic (CC BY 2.0)

Chain Bridge (map) had three lanes stretching across the Potomac River between Arlington and Washington, with the middle lane reversible. Only a single sign told motorists about the unusual situation (Street View). Presumably daily commuters traveling over the bridge during critical hours would already understand the situation. Woe to the poor visitor who happened to cross the bridge at an inopportune time and not see the sign.


A Machine Does All the Work


Lane Mover
Roosevelt Bridge, Washington, DC, USA
via Google Street View, August 2014

Another Potomac River bridge between Arlington and Washington, the Theodore Roosevelt Bridge (map) offered a better solution. The reversible section had a concrete barrier to keep drivers from making a mistake. An odd little machine moved the barrier twice a day to accommodate commuters. This unusual arrangement was created by Lindsay Transportation Solutions.

The moveable barrier system enables the DOT to quickly reconfigure traffic lanes and directional capacity on the bridge in less than 15 minutes (the bridge is just under one mile in length). The Barrier Transfer Machine (BTM) safely transfers the barrier one or two traffic lanes at speeds from seven to ten miles per hour. A magnetic tape grooved into the pavement guides the BTM and ensures precise placement of the barrier wall.

That seemed a lot safer than signs or overhead lights.


Completely Reversible with a Sign


IMG_4012
IMG_4012 by bankbryan, on Flickr
Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0)

Some of our local roads were completely reversible. The Rock Creek Parkway (map) — actually called the Rock Creek and Potomac Parkway in official terms, which I didn’t know until a few minutes ago — operated with two lanes in both directions most of the time. However in the morning all four lanes headed towards Washington and all four lanes returned traffic to the suburbs in the evening. Monday through Friday. Except Federal holidays. Make an error reading a sign (Street View) and find oneself heading towards the wrong way on a four-lane highway.

I would stay away from here on Columbus Day. Federal government employees are about the only people who get the day off. Imagine everyone else forgetting about that quirk and thinking it was a normal Monday commute. Yikes!


Completely Reversible and Safer


Interstate 395 - Virginia
Interstate 395 – Virginia by Doug Kerr, on Flickr
Creative Commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0)

A stretch of Interstate 95 and Interstate 395 (map) from Northern Virginia into the District featured two High Occupancy Vehicle (HOV) lanes that switched directions for the morning and evening commutes, sandwiched between and completely separate from the regular highway lanes. These are being converted into High Occupancy/Toll (HOT) lanes although the concept will remain largely the same.

These seemed considerably safer. Barrier arms blocked access to ramps that led to these special lanes so that cars traveling in the "wrong" direction couldn’t make a mistake. The arms raised when the lanes reversed and it was safe to travel that direction again.

There were several more reversible lanes in the area that I didn’t have space to mention. Also Wikipedia had an entire article devoted to reversible lanes in other parts of the world so I imagined they were rather prevalent. It was funny how I’ve grown so used to seeing them that I never considered how weird they seemed conceptually.

On November 5, 2014 · 3 Comments

3 Responses to “Reversible”

  1. Philip Newton says:

    Hamburg, Germany, has this in the tunnel under the Elbe.

    There are four main pipes, each with two lanes. (Though it seems that at least one pipe is always closed; at least things are better than before they build the fourth pipe.)

    Generally, three lanes are for northbound traffic and three lanes for southbound, with the outer pipes that are in service being one-way and the middle one being one lane in each direction. Red crosses and green arrows show which lanes can be used, not only in the tunnels but also on the approach. Barriers across the approach lanes can also be used to open up either three or four lanes (all four would be in use if there are four lanes through the tunnels).

  2. David Kozina says:

    About 6 months ago a section of a major East-West street in the Salt Lake metro area was converted in this fashion, with red X and green arrow indicator signals over the street.
    I think the rush-hour traffic probably did justify the change – however, I find in my case that when I have to drive on that street AT NIGHT, the GLARE from all of the GREEN arrow signals down the road and off into the distance tends to obscure the even more important (but less visible) red traffic signals at intersections. When all you notice is green ahead, well I guess it means go…
    I wonder how much night-time color perception was a consideration in the design of the signals.

    (Similar comment could be applied to vehicles with blindingly brilliant blue-white headlights – they almost make my eyes bleed – yeah I certainly notice them, but not much else for about a minute after they go past.)

  3. brian obrien says:

    The Golden Gate Bridge
    Reversible Lanes and Head-on Crashes.
    After 30+ years of debate Iconic Bridge to get Movable Barrier in January

    On January 10-11, 2015 the Golden Gate Bridge will be closed to all traffic and a Movable Median Barrier will be installed. (depending on weather)

    Since 1984, total annual traffic crossing the Golden Gate Bridge has been between 38 million to 42 million vehicles. The roadway is 1.7 miles long with six narrow lanes: two, 11-foot wide curb lanes and four, 10-foot wide lanes with no shoulders.

    Opposing directions of traffic are separated only by 19-inch tall, 4-inch diameter plastic tubes, spaced at 25-foot intervals.
    The tubes are manually placed in sockets in the roadway to identify the northbound lanes and southbound lanes and are reconfigured several times per day based on real time traffic.

    The Movable Median Barrier (MMB) system includes about 13,340 feet of barrier consisting of 12-inch wide and 32-inch high steel clad units filled with high density concrete tightly pinned together to form a semi-rigid median barrier. The system also includes two barrier transfer machines, aka “zipper” trucks.

    The installation of the one-foot wide MMB would virtually eliminate crossover collisions.

    http://goldengatebridge.org/projects/MoveableMedianBarrier.php#Timeline

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