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Interchange Index
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.