The photo shows the problem. The tree in question is leaning over the road and does show signs of damage to the trunk where it has clearly been hit by vehicles - although nothing recent. The tree's presence pushes larger vehicles out to the left hand side of the inside lane on the roundabout and there is always the risk that a driver unfamiliar with the layout of the Green could wind up hitting the tree. If the driver was "making lawful use of the highway", then now the council is aware of the problem, there is no defence to an insurance claim, leaving the council liable for the full cost of repairs to a damaged vehicle. Worse, there is always the potential for a collision to cause injury, putting any financial loss into the shade. Given that this is an A road, with junctions with two major B roads and a major route into the city centre, the risk of collision is significantly higher than a similar tree on a residential road not often used by goods vehicles.
Birmingham is very sensitive to this - and rightly so - since a fatality in Kings Heath a few years ago and the A38M case which saw a council officer facing trial over the death of a motorcyclist who had hit a drain on the Expressway.
There is a clear problem - so can anything be done to save the tree by changing the island layout? It would be possible to change the original line of the Green to create some additional space for grass, but that would change the road alignment and would actually need to run for about 30 metres before the tree to adjust the line of traffic smoothly. Added to that, the works would be carried out over the tree roots themselves, risking damage and possibly dooming the tree anyway. The work would not be cheap - with costs suggested of over £30,000.
Nick made the point that the tree wasn't put in the right spot in the first place - it was planted too close to the kerb. It is also not a great street tree - horse chestnuts are better suited to parks and this one would have thrived in a more central spot on the Green. There is also the risk that the tree will contract bleeding canker that has already killed a horse chestnut on Henbury Road.
The good news - and there is good news - is that the tree will be replaced by two new ones, better located on the Green itself and that the new planting should be completed this winter as part of the normal planting season. Amey don't use saplings, they plant trees that are about two years old. I'm sorry to see this tree go, but we have been able to get something more out of it.