Northlake BC-CS 9807167--16--1998, 2:,.51PM FRJ;;ik[ ~ I:::'. 1
DECELERATION LANES
Rioht Turn Deceleration Lan_a~ '
'A deceleration lane for right turns into a driveway eases th' negative im act that a drive h
. . · P as
on the flow of traffic on an adjacent arterial. ~uch · provi n enables right~turning traffic to
slow down to turn, without impeding the flow of through raffle. It also reduces the risk of
rear-end accidents.
A deceleration lane should be considered on arterials v~ith a~ ~rage operating speeds of 35 mph
or more, if the following conditions apply:
1. The average peak hour inbound right turn vc ume is at least 75 vehicles.
2. Where several successive driveways meet c,)ndition 1, and driveway spacing
is not adequate To avoid encroachment of the right turn lane on another
driveway, a continuous right turn lane shouh be used.
3. A continuous right turn lane should be co~ ,stdered at e location where 20
percent of the directional volume on the arte~'ial makes a right turn.
For signalized driveway intersections, lane requirements should be based on a capacity
analysis.
Rieht Turn Lena Lencrth
Deceleration lanes should be of adequate length to permit ,,~afa deceleration from the design
speed to a stop within the deceleration lane. Traffic may 'l~e assumed to leave the through
lane at 15 mph below the design speed. The total decelerati ~n lane length includes the length
of taper. It also depends on the speed of the vehicles on the roadway. Table 3.10 (Reference
1 ) shows the desired length for various design speeds.
TABLE 3.10
RIGHT TURN LANE LEN~3TI~
Arterial 150 - 250
Collector 25-35 50- 150
The recommended taper lengths for left .or right turns an displayed in Table 3.11. The
transition should be accomplished using reverse curve geor~ etry.
7--16--1998 2:S2PM FROM
TABLE 3.11 ., ,
TRANSITION DISTANCE FOR DEC !LERATION
100- 150.
Collector 1 O0 - 150
The total right turn lane length is the summation of the deceleration length (Table 3.10) and
the transition length (Table 3.. 11).
MEDIAN OPENING
i MEDIAN OPENINE} SPACING
i'
The location of openings in a median to allow left turn in~;'ress and egress movements, at a
driveway or local street is a function of the type and opes'sting speed of the roadway; the
volume of traffic expected to make the left turn movements and the location relative to other
intersecting streets, driveways,, and median openings.
Median openings may be permitted on divided thoroughfares at intersections with public
streets and/or driveways. The order of priority.for determining where median openings should
be located is as follows:
1. First Priority - Designated Thoroughfares
2. Second Priority - Minor Streets
3. Third Priority - Driveways
Median openings will be provided at ell intersections with d; signeted arterials and colleqtors.
They will normally be permitted at ali intersections with mi. ,or streets, with priority given to
minor streets that serve collector functions. No median o; ening will be permitted at minor
streets or driveways if specific conditions create an unl afc intersection. Vertical and
horizontal sight distance must meet minimum standards, as I~reviously specified in this report.
No median opening will be allowed to serve either alleys or einergency access easements, and
the minimum distance of an opening to an intersecting public street will be governed by the
combined left turn lane design requirements for that intersection and the median opening, as
twell as the functional classification of the two intersecting ~treets;
Median openings should not be granted unless all of the icl =wing conditions exist:
1. The property to be served has a'driveway Bt the median opening and is a
significant traffic generator With demonstrat4 cl or projected trip generation of
not less than 100 left turn ingress or egress vehicles during the 'peak hour.
(Reference 7)