M A
6 1 : 1 0 : 9 8 1 0 2 / 6 1 / 5 HOW A DIVERGING DIAMOND WORKS
OVERVIEW
M
H
O
T I R
R T - U 8 A F O 3 O INTERSTATE M
S N P P Y O 3 M 83 T O R 8
A O - T I R R H K
TO TO SHREWSBURY STEWARTSTOWN
851 851
B
A
L
T T INTERSTATE
I O
M M
H I R 83
O - T O 8 A
R 3 R M R
F
S O
P E O N P T U
3 O M T
8
A H -
I
R
A diverging diamond interchange (DDI) is unique from a standard diamond interchange in that the side road traffic (PA 851), crosses over to the left side of the road at a signalized intersection prior to the bridge. This allows direct left turns from the off-ramps to merge and allows for a direct left turn on to the on-ramp. The side road (PA 851) traffic crosses back to the right side of the road at a signal beyond the bridge.
The DDI configuration has an operational advantage over the standard diamond in that it has only 2 phases per signal cycle versus 3 phases. This allows the DDI to provide more green time to traffic alleviating congestion. Additionally, because of the direct left turns, there are fewer conflict points than a standard diamond interchange which reduces the crash rate and crash severity.
PA 851 CROSS TRAFFIC
M
H
O
T I R
R T - U 8 A F O 3 O INTERSTATE M
S N P P Y O 3 M 83 T O R 8
A O - T I R R H K
TO TO SHREWSBURY STEWARTSTOWN
851 851
B
A
L
T T INTERSTATE
I O
M M
H I R 83
O - T O 8 A
R 3 R M R
F
EASTBOUND PA 851 S O
P E O N P T U
3 WESTBOUND PA 851 O M T
8
A H -
I
R
PA 851 traffic crosses over to the left side of the road at a signal prior to the bridge. It crosses back to the right side at a signal beyond the bridge.
PA 851 TO I-83 MOVEMENTS
M
H
O
T I R
R T - U 8 A F O 3 O INTERSTATE M
S N P P Y O 3 M 83 T O R 8
A O - T I R R H K
3 TO 1 TO SHREWSBURY STEWARTSTOWN
851 851
2 4
B
A
1 PA 851 EAST TO I-83 NORTH L
T T INTERSTATE
I O
M M 2 PA 851 EAST TO I-83 SOUTH H I R 83
O - T O 8 A
R 3 R M R
3 F PA 851 WEST TO I-83 NORTH S O
P E O N P T U
3 4 PA 851 WEST TO I-83 SOUTH O M T
8
A H -
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Traffic from PA 851 can turn right prior to the first signal to enter the on-ramp (movements 2 & 3) or turn left immediately following the bridge (movements 1 & 4).
I-83 TO PA 851 MOVEMENTS
M
H
O
T I R
R T - U 8 A F O 3 O INTERSTATE M
S N P P Y O 3 M 83 T O R 8
A O - T I R R H K
3 1 TO TO SHREWSBURY STEWARTSTOWN
851 851 n g d . s t n e 4 m B e v o A M 2 - I I-83 SOUTH TO PA 851 EAST L D 1 D
_ T T INTERSTATE g t
M I O b
M M u 2 I-83 NORTH TO PA 851 EAST H P I R 83 _
O - T D 8 O A A O
R 3 R R M R _
F 1 3 I-83 SOUTH TO PA 851 WEST S O
O P C E
_ O N
P 4
T T
I U
3 X O M
E 4 I-83 NORTH TO PA 851 WEST T -
8
A 3
-
8 H
I I
R _ 9 9 2 8 5 \ 3 7
0 Traffic from the off-ramps can turn right at a signal directly on to PA 581 (movements 2 and 3) or turn left at a signal directly 0 3 5 0 d
\ on to PA 581 (movements 1 & 4). t e l m a h j \ 1 0 w p f g \ g n i k r o w w p
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