Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-08-09
TRAFFIC PRACTICE
| TRENDS DESCRIBED
N. o. EIdridge, Through
American Road Builders,
Lists 10 Points.

Indications as to trends IN trafhc
practice In cities and the vehicle capa'
city of streets are given in q report Of
the Trafic Committee Of the American
Road Builders Association, NJ. o. Ed
ridge chairman.
The following descriptive statements
are indicative Of the trend toward
standard practice:
/. A minimum width of 80 feet Il
required for two lanes Of trafiic witt
parallel parking. For each additions
krafic lane add 10 feet.
2. The width of traffic lanes WIZ o.
controlled in some measure by develop
fnents In the width Of vehicles. Ter
Ieet seems ample width, except on curves
OF less than 400 feet radius.
3. Parking widths should be the SAME
"A q trafic lane to provide an add
ticnal lane when no parking Is allowed.
Fan Angle Parking.
a.. Angle parking should not be per-
5. franc capacity should be defined
M the number of vehicles passing
giyen point in q given time. Another
dennition Of capacity that was advanced
Is that of car miles per hour per trafnc
lane, which introduces the element OF
congestion.
6. The idea is advanced that through
trafflc in any lane has the right Of way
over other vehicles performing any
other inaneuyer The public accetp-
ance of this simple conception might
result In q considerable reduction In
accidents.
l. The assumption that the driver
ahead will not use anything like his
full braking capacity without warning
d evidently true, and leads to car In
teFvals Of less than those assumed In
theoretical computations Of traffic lane
capacity.
Congestion Defined.
q. CONGESTION Is defined as q condi-
ton on the road when cars have DIM
Guilty in passing for . period Of one
minute.
Q. increased width does not proper
tionately increase the carrying capacity
Of 4 street because of the weaving from
one lane TO another.
TO- Fast trafIlc should be separated
from SLOW trafiic where possible.
IL. The relative capacity Of two, three
and four lane roads appears TO be In
the ratio of I E: III 91z. For two
lanes, 1000 vehicles per hour. In both
directions, passing a given point: for
three lanes, 1000 vehicles; for four lanes
the capacity was not reached at $500
This capacity was established by A. N
johnson and reported to the Highway
Research Board.
ia. A speed of 2s miles per hour on
city streets appears TO produce the
greatest capacity with reasonable fac
tor Of safety.
IL. The frequency Of intersections
undoubtedly materially affects street
capacity. Short blocks often do not
provide glficient storage space for carr
waiting at an intersection.
Maximum vehicle width.
Il. The maximum width of vehicles
of e6 inches. which has been almost
universally adopted, Is ample, with the
possible exception Of some vehicles used
In industrial work. At the present time
there Is not sufdcient number of We
hicles wider than e6 inches to modify
trafnc lanes for them. However, the
future deveiopnent OF industrial We
hicles should be kept In mind,
rs. Six-whee1 trucks and pneumatic
tires reduce concentrated loads on high.
ways and impact stresses and permit the
hauling of relatively heavier loads.
16.. II IS practical 70 prohibit COM
nerrial vehicles from certain streets In
some citieg, and the practice seems TO
IL The routing Of through and heavy
trafic appears 70 be practical. and Is q
desirabIe measure In reducing conges-
ton.
10. For rate Of now Of trafic Of
less than 10 miles per hour, accom-
panied by congestion, parking should be
eliminated during hours of congestion.