Civil Engineering Reference
In-Depth Information
The left and right turn lanes should be long enough to prevent spillback onto the
through lanes
Each auxiliary through lane should be at least 300
400 ft long on each side of
-
the intersection, exclusive of taper
For a safe pedestrian crossing a center median refuge area of at least 5
6ft
-
should be provided.
17.2.2.2 Indirect Left Turns
Removing and relocating left turns from signalized intersections reduces congestion
delays and crashes. Intersection designs that divert or reroute left turns can simplify
traf
c signal phasing and reduce intersection delays. Examples include New Jer-
sey
'
s
“
jughandles
”
and Michigan
'
s
“
Indirect Left-turn Strategy.
”
Both designs
convert left turns into right turns
—
simplifying the traf
c signal phases.
This design requires left turns from the arterial to turn
right, and then enter the cross road. The cross road can be entered from either the
near side or far side of the intersection. Rerouted left turning vehicles cross the
arterial road on the cross street green time. Jughandles may reduce overall travel
time to cross the intersection by 4
New Jersey Jughandle
—
although left turn
movements experience added delays from an increase in the number of stops. This
operation (see Fig.
17.3
) requires a large area to provide suf
45 % during peak conditions
—
-
cient queue space on
the ramp connecting to the cross street.
The Michigan Indirect Left Turn Strategy
(sometime called
)
has been applied to highways with wide medians for more than one half century
[
6
]. Figure
17.4
shows the arterial and cross street movements accommodated
by this strategy.
“
Median U Turns
”
guration of the intersection to include (1) right
turn lanes; (2) jughandles instead of left-turn lanes; (3) building under/over passes
where it is necessary to separate crossing
This strategy entails the recon
fl
flows; and/or (4) establishing roundabouts
where traf
c signals are not ef
cient in controlling intersecting
fl
ows
—
especially
where more than two streets intersect.
A more recent variation of this treatment
—
applied as
“
Superstreets
”
in North
Carolina
—
works well when the arterial road has the dominant
fl
ow, (where there
are and no pedestrians). This treatment, sometimes called the
“
Restricted Crossing
U Turn (RCUT)
is shown in Fig.
17.5
.
All the cross street through traf
”
c entering the Superstreet must turn right, then
proceed several hundred feet before making a U turn like the Michigan treatment.
Side street intersections are signalized where they enter the arterial, and sometimes
the U turns are signalized as well.
Both concepts allow two-phase traf
c signals along the main roadway, with the
arterial getting most of the green time. The safety and congestion relief benefits of
