The trumpet is the most traditional way of grade-separating a three way junction - this is your basic free-flowing way to end one road on another. It is the sister of the cloverleaf, as both hail from the same period of early grade separation in the 1920s, and as such are heavy on land use and light on construction work - both use only one bridge.
Where to Spot Them
Usually found connecting a motorway to a short spur, but from time to time at busier locations too.
- M4 spur to Slough
- M5 spur to Brent Knoll
- M6 spur to South Lancaster
- M9/M876 (E)
- Low construction costs for bridges/underpasses.
- On tolled roads (such as the M6 Toll, where numerous trumpets are found) the trumpet is a cost-effective way of getting all traffic in one place for toll booths.
- Disorienting to navigate for those driving in the direction that uses the loop.
- Expensive to build in places with high land values, and leaves a redundant patch of land within the loop.
- Scaling down the interchange often results in a more dangerous interchange - the M6 at Stoke frequently suffers congestion from articulated lorries that have tipped over.
Very occasionally the trumpet can be made into a four-way free-flowing junction with one of the arms only for straight-through movements. There is one in New Brighton on the Wirral; a more famous variation is at Chevening. More frequent than this is the trumpet where all four sliproads terminate on a roundabout, such as M621 junction 4 and M6 junction 15. One variant in central Liverpool has three movements going around the looped side, as there is a lack of space for one of the left turns. And an unusual (probably unique) example exists on the A41 in North London that does not allow a right turn into the terminating road.
With thanks to Phil Reynolds and Simon M4Man for information on this page.