Evening star., 1934-03-11

out the inequity Of many special as
sessments of the past.
On the design of the structures,
several variations are suggested to
meet special conditions. The type
proposed as standard for the Chicago
system would be constructed in exist
ing streets on a pavement supported
by pillars. There would be four mov-
ing traffic lanes with provisions for
adding two more lanes when more
width is required.
Minimum Of Delay.
The main argument advanced for
this type of elevated highway is that
1t would involve q minimum of acqui-
sition Of private property for right Of
way, thus saving money and delays
In construction. Figures were quoted
to show that this would be less costly
than pavement on a sand fill be-
tween a retaining wall and an exist
ing railroad embankment, a design
which has been generally accepted as
the most economical and feasible Of
elevated highway proposals.
The most novel feature Of the pro-
posed standard design-the feature
that accounts for the record low esti-
mates for elevated highway construc-
ton costs-is an open grid pavement
OF steel or concrete, Of high strength
and light weight. This pavement
would be much lighter than the con-
ventional concrete slab and the cost
of foundations, pillars and other sup
ports would be substantially lessened
Other recommendations are cited
for the grid pavement. II would admit
light and air to the street below
Without any maintenance, 1t would
always be free from snow and ice. No
drainage equipment would be neces-
sary. The grid pavement would af-
ford far better traction than any con-
ventional pavement. the survey de-
clareS.
Railings Three Feet High.
The outside railings Of the pave
ment would be about three feet high
with gradual inside slope so that
only the tire would touch II an auto
mobile were to drive too close to the
side. A curb in the center would
separate trafic bound in opposite
directions.
The proposed lighting is as much
a novelty as the open grid pavement.
Electric lamps would be sunk in the
center curb with rays directed onto
the pavement away from drivers
eyes. The outside railings would be
used as reflectors to get a maximum
of utility from every light.
Ramps would be provided at con-
venient intervals for entrance and
exit from the structure. These would
be one-way drives to insure q maxi
mum of safety. At terminals or other
places of heavy traffic, instead of
widening a ramp, several Of them
would be built so as to distribute the
vehicles on the ground level streets.
Approaching each ramp would be
special lane for acceleration or for
deceleration so that the through traf-
fic could maintain a speed of 40 miles
an hour, or higher, without Interrupt
ton.
Cost s4s1, 900 \ Mile.
The cost of such structures is esti-
mated at s431, 900 a mile. This would
provide for passenger cars only, and
such is the recommendation of the
McClintock survey. Providing for
truck traffic, which constitutes only
10 per cent of the city's traffic. would
increase the costs so per cent. The
freighters would benefit. however, by
removing passenger traffic from their
surface routes.
This estimate Of S43l 900 per mile,
the report points out, is only 15.5 per
cent of the cost of equal traffic capac-
ity gained in street widenings. as IL
lustrated by the additional traffic lanes
which were obtained in the Western
avenue, Ashland avenue and La Sale
street improvements.
A comparison is also made OF the
cost of paving two parallel streets
without widening to be used for one
way traffic systems and it was found
that the cost per mile Of the elevated
highway is only s92 ,208 more than
one-way surface pavement OF equal
traffic capacity.
For this se2, ,2O8 mile the motorists
are offered facilities that will cut
travel time in half with safety. Studies
indicate that 70 per cent Of all acci-
dents on surface routes would be
physically impossible on the elevated
highways.