There is a speed limit change from 40 to 30 about 300 feet before the bridge to the west and the road then narrows, but an awful lot of people ignore it this just keep on going at 40 or more when going down the incline to the bridge.
Therefore coming from the west (which I think this cement mixer was?) you can get caught out on the bend as it isnt designed for 40+ mph and the lane is not that wide, plus there is the bridge wall on the side and not to mention the station entrance on the other side which is a tight bend so people often take it very wide. You see a lot of vehicles coming the the west that end up a few feet into the wrong lane for this reason and sometimes have to swerve back into their lane. Also there are traffic lights to the east and often cars have to queue on the bridge as a result, speeding into the area just means trouble!
If you are a large lorry and there is another lorry on the bridge or someone is turning out of the station road (into your lane or the other lane) you could easilly be in some trouble unless you are going slow as there really isnt much space on left hand side if you are heading east, as the footpath is on the other lane.
That is what I would suspect happened assuming no mechanical error, went round the (semi blind) bend too fast, maybe on the wrong side of the lane slightly coming out of the slight bend, or meet someone just pulled out of the station road to go east and still accelerating, cement mixer driver had to swerve, back end of the mixer kept on going due to weight, and loss of control as a result.