Complex sentence: Not all of British transport operational standards have been metricated--in the railway industry, although metric units and distances are used on many new systems, most pre-existing systems have retained imperial units, especially for speed and distance.
Split into simpler sentences: Not all of British transport operational standards have been metricated--in the railway industry. Metric units and distances are used on many new systems while most pre-existing systems have retained imperial units, especially for speed and distance.