By Peter Samuel
Tokyo's Slim Xprswys
Tokyo is proof that there's no need to stick rigidly to the AASHTO (U.S. state highway officials) dogma that the only good highway lane is a 12 foot lane (3.66m). 12 foot has been the American ideal lane width since it was adopted by the Pennsylvania Turnpike in the 1930s, and was embraced in the 1950s as a federal standard for the 41,000ml (66,400km) interstate system built between 1956 and 1995. Most of Tokyo's toll expressway system (22 routes totalling 154ml or 248km as of 1/1/95) is built with 3.25m lane widths (10'8"). Called Type 2, Class 2 the system is designed with curves down to 120m (394ft) radius, sight distances as low as 75m (246ft), and maximum grades of 8%. U.S. grade max is 4%.
A Japanese Class 2 expressway of this kind has a design speed of only 60km/hr (37mph) and according to Hideo Tokuyama head of the planning division of the Ministry of Construction (and at present a visiting fellow at Turner Fairbank) most of the traffic flows at 70 to 80km/hr (44 to 50mph). Certain curves and ramps on the system are posted at 50km/hr (30mph), he says, and there are generally lower speed limits (10km/hr or 6mph lower) for trucks than for cars. The marked 3.25m lanes of the 2/2 standard Japanese expressways are supplemented by "shoulders" of 0.5m (20") on left and right of the side lane markings, so between kerbs there is a 2-lane 7.5m (24'7") roadway/carriageway. This extra edgespace on the old Tokyo system has allowed it to be open to all vehicles including long tractor-trailers.
Tokuyama says the inner sections of the Tokyo network were built at great speed to be open for the 1964 Olympic Games. High real estate costs, the need to minimize property aquisition, and to get as much as possible built for the Games played a part in developing Tokyo's expressways as a relatively low-speed system.
The Hanshin Expressway Corporation that built the urban tollways in the Osaka/Kyoto area, Japan's second largest metro area, has many similar tight, low-speed expressways. There are 4-level all-way direct-connection interchanges in the Hanshin system with a very small footprint due to very sharp ramp curves, and there is one famous off-ramp (at Umeda) that goes right through the middle of a circular plan highrise office building. That building also has a helicopter pad on the roof, making it an "intermodal facility" nothing in the U.S. can match!
Most of the new toll expressways in the Tokyo metro area are being built to a more forgiving set of standards. Called Type 2 Class 1 expressways, these have a design speed of 80km/hr (50mph) with 3.5m wide lanes (11'6"), 230m (755ft) radius curves, but still have steep 7% max grades and 110m (360ft) min. sight distance. The latest Tokyo Bayshore expressway also has an outside breakdown shoulder of 2.25m (7'4") but is unusual in that.
In recent years Japan's tight geometry has been blamed for accidents and new intercity tollways are being built to quite generous standards. Most have 3.6m lane width (11'9") indistinguishable from the U.S. interstate standard. The tollway between Tokyo and Osaka (about 300ml or 490km) is being doubled. The existing overcrowded 4-lane Tomei/Meishin highway is being supplemented by a new 6-lane tollway on a completely new alignment for most of its length, avoiding the bump north to Nagoya metro area . This New Tomei-Meishin tollway is being built to geometric standards of curvature and sight distance more common to the German autobahns than to any U.S. highways and the lanes will be very generous width 3.75m (12'4"). The operator Nihon Doro Kodan (Japan Highway Public Corporation) expects to post a 140km/hr (88mph) speed limit on this road when it opens in a year or two.
The Honshu-Shikoku Bridge Authority is constructing the world's longest suspension span (1990m, 6527ft) on the 3.9km (2.4ml between cable anchorages) long Akashi Kaikyo bridge in the Inland Sea west of Osaka and it is being built with a 6-lane divided section of two 10.75m (35'3") roadways/carriageways, just a lane stripe shy of full U.S. AASHTO standards. The Akashi will also have a mountable outside shoulder of 2.5m (8'3"). The Golden Gate bridge has 6 lanes on a single 62ft (18.9m) roadway, making for tight lane widths of only 10'4" (3.15m). New York's old Hudson River tunnels are tight, the Holland tubes having really claustrophic 20ft (6.1m) 2-lane roadways and the Lincoln 21'6" (6.55m). The Holland lanes therefore must rank as very tight indeed at 10ft (3.05m) and the Lincoln lanes are only a bit better at 10'9" (3.28m), a common standard for pre-1956 U.S. cars-only parkways and inner area expressways. The Hudson river tunnels run traffic at Tokyo Metro Expressway speeds of around 45 to 50mph(70 to 80km/hr.)
U.S. traffic engineers say that going between 11ft (3.35) and 10ft (3.05m) lane widths something that is often done in work-zones decreases speeds markedly while increasing accidents, but they say between 11ft and 12ft there is little detectable impact on driving behavior or safety. Many U.S. metropolitan area expressways originally built to 12ft (3.66m) lane widths in the 1960s are being restriped down to 11ft (3.35m). This has been done on many stretches of Los Angeles and San Francisco Bay area freeways (the native term) in order to make room for new HOV (high occupancy vehicle) lanes. Shoulders have also been sacrificed to squeeze in an HOV-lane. The same was done to expand I-75/85, the main north-south expressway in the Atlanta metro area, from 12-lanes to 14-lanes width recently. In free flow conditions the traffic runs at about the same speed on 11ft as on the old 12ft lanes at 67 to 72mph, 110-120km/hr, and seems to be quite unaffected by posted speed limits unless police are visible. Accident rates don't seem to be increased, state engineers in charge say, by going down to 11' though they like to keep 12' lanes on the outsides for trucks. Most U.S. toll roads seem to be sticking to standard 12' (3.66m) lane widths. (Japanese contacts: Tokyo MEPC fax 81 3 3503 1806, Nihon Doro Kodan fx 81 3 3506 0346, Hanshin Corp fx 81 6 251 6933, Honshu-Shikoku Bridge Authority fx 81 3 3578 9298)