The cost and disruption of lowering the road would be substantial. It would also create other problems of connectivity and safety.
Experience in other areas of the country show that bridges, which involve ramps to make them accessible, tend to be less attractive to users. Providing a bridge would mean some people would still seek to follow the most direct crossing in an uncontrolled way, which would be more dangerous.
Super crossings have been shown to be successful on roads with the same or more traffic. They also act to reduce speeds of vehicles which in turn improves safety and the local environment for residents. This is seen at Tregolls road which has significant traffic flows but still provides an attractive environment for residents. Reducing speeds on routes does not reduce the capacity of the route or increase congestion. Research shows it actually improves the quality of the environment, one of the objectives of the Garden Village proposals.