Railroad operation in the United States - and, to a degree, in Canada - is dominated by freight. Long heavy freight trains are the order of the day - often running enormous distances (Chicago - Los Angeles, for example).

At the moment there is little passenger operation - but this may change. For a range of reasons, higher-speed passenger service is being studied in a number of places.

Mixing trains with different speed characteristics eats capacity - it's much more efficient, in capacity terms, to have all trains running at a constant speed with a constant stopping pattern. So the proposed super-imposition of more passenger trains running faster has caused warning bells to sound among the freight railroads - who own almost all of the rail infrastructure. Understandably, they want to ensure that they keep their present level of capacity: equally, they do not want to be worse off financially or to have to bear any onerous insurance liabilities.

This has brought to light some differences in standards.

Norfolk Southern will only allow 79 miles/h (127 km/h) on existing freight tracks: higher speeds need a separate right-of-way. Union Pacific is prepared to allow 110 miles/h (177 km/h) on a case-by-case basis. BNSF will allow 90 miles/h (145 km/h) and wants higher speed trains to use a separate track: CSX says the same, but insists on a 30 foot (10 metre) separation between the tracks.

Since these standards are different, are they all correct? Are they all sound? It does sound rather as if someone has put a wet finger in the air, rather than applying science and logic! Maybe someone - perhaps the AAR (American Association of Railroads) with the help of the UIC (International Railway Association) ought to do some kind of risk assessment to see what the parameters are - what are the risks, how can they be managed, and what kind of safeguards are reasonable.

Waht are the risks of mixing high speed passenger and heavy freight? What are the optimal clearances - so that, for example, double-stack container trains can safely work on an electrified railway? What are the insurance needs?

There is plenty of experience around the world of operating freight and high-speed passenger trains on the same infrastructure: let's draw on that to ensure that all possible lessons are learned before we move on to sub-optimal solutions. Those cost money!