We know what caused the Potters Bar rail crash, but we still don't know who. Jarvis, which is responsible for the track, claims to have evidence that the faulty points were sabotaged – a possibility highlighted in Building last week, despite being dismissed by rail experts. Investigators seem adamant that incompetence or human error was to blame (see news). In pressing the sabotage theory so ardently, Jarvis is playing a dangerous game. It risks being seen to place more importance on salvaging its share price and forestalling corporate manslaughter charges than finding out why seven people died. However, one might equally argue that investigators have been too quick to rule out sabotage and, in so doing, to demonise Jarvis. Perhaps the sabotage theory is just too gruesome to contemplate, even though points have been tampered with before, and trespassers have made 1200 incursions onto the East Coast Main Line in the last year. Against this background, Jarvis can hardly be blamed for wanting to be in on the testing of the nuts.

Whatever did happen at Potters Bar, the political reality is contractors will come under intense scrutiny in the coming weeks. For once it was hard to argue with transport secretary Stephen Byers, who called on Tuesday for "fundamental change". He was speaking in the wake, not just of the crash, but of a court's verdict that a 22-year-old student who had been working unsupervised on the railways had been unlawfully killed. There have been too many disasters now to resist change. Maintenance firms must, like everyone in construction, move towards airline standards of safety. They need to step up the recruitment of skilled staff – from abroad, if necessary – and train them harder. If the costs have to be shared with Network Rail, so be it: safety comes first.

Byers' comments were interesting for what he did not say. He did not suggest that contractors be removed from maintenance. Instead, he appeared to endorse Network Rail's desire to extend contracts from five to 15 years; and he talked of shared incentives and selection on best value rather than tougher penalties for safety breaches. This is understandable. The current penalties for poor track performance are draconian enough, with negligent firms facing the loss of their contracts. Jarvis, for example, is responsible for maintaining more than one-fifth of the network. Dismissal would be devastating, which is why its share price collapsed more than 200p in the days after Potters Bar. In any event, no serious business knowingly kills its customers, with the possible exception of the tobacco industry.

Amid all the hysteria over Potters Bar, it was timely of the Construction Industry Council to publish a sober report on transport last week. This concludes that Labour's 10-year improvement strategy has too many inconsistent goals, such as improving speed and safety. This is especially true of the railways, where a network creaking from decades of underinvestment is expected to carry sharply increasing traffic. Potters Bar gives Byers an ideal opportunity to acknowledge that the infrastructure can't be fixed by 2010, and to set what the CIC calls "realistic objectives". Meanwhile, says the council, projects of strategic importance should be fast-tracked. Yes, and perhaps they could be funded through the toll motorways just proposed by Tony Blair's transport guru Lord Birt. At a time like this, it would be utterly perverse to invest in roads and not rail.