Interchange Index
I-95, US 1 Bypass, US 4, NH 16, and the Spaulding Turnpike
Portsmouth, NH
"The Portsmouth Circle"
Overhead Picture from terraserver-usa.com
Overview: The main expressway running from southwest to northeast is Interstate 95. US 4 and NH 16, running on the Spaulding Turnpike, runs northwest from this interchange. US 1 Bypass, a through route through Portsmouth and Kittery, runs southeast and northeast out of the traffic circle (known as Portsmouth Circle). On I-95, the northbound exit for the Portsmouth Circle and the single southbound exit are both numbered Exit 4. The northbound ramp to the Spaulding Turnpike is Exit 5. Exit 6, a single northbound offramp to Woodbury Ave., is also visible just north of the circle.
Interchange Description: The main section of this interchange is a three-way fully directional split on Interstate 95. Going north, one can exit left to the Spaulding Turnpike or right to the Portsmouth Circle. The ramps from I-95 merge with the Spaulding Turnpike at another fully directional split. Both sides of the three-way split and the Spaulding Turnpike's split have ramps to allow for the missing right-turn movements, but not the left-turn movements. The remainder of the Spaulding Turnpike and US 1 Bypass intersect with the I-95 ramps at the Portsmouth Circle, just east of I-95.
Advantages: Although it seems as if all of the splits here are missing ramps, this interchange actually has no missing connections. The use of a traffic circle in this design eliminated many bridges and ramps in what would have otherwise been a very complex five-way interchange. The ramps directly from I-95 northbound to US 4 eastbound and US 4 westbound to I-95 southbound are technically redundant because of connections at the traffic circle, but they cut down on traffic through the circle and through the at-grade intersection at Northwoods Road, which crosses the turnpike between the split and I-95. Outside of the traffic circle itself, there is no "weaving" involved in the interchange.
Disadvantages: Because of the missing left-turn ramps at the three splits, some movements through the interchange are rather circuitous. For example, traffic traveling from I-95 southbound to the Portsmouth Circle must exit to the US 4 ramps, take a right turn onto US 4 eastbound, and then go through the intersection at Northwoods Road before getting to the circle. I-95 also has a left exit and a left entrance at the three-way split, which are often frowned upon on Interstate highways.
Corrections? Suggestions? More information is always welcome.
Suggestions for more interchanges to cover on this site are great too.
Contact the author, Dan (known as DanTheMan on misc.transport.road):
twowheel@email.com
