High-speed rail
Road-rail parallel layout
#### Road\-rail parallel layout

[thumb\|A German high\-speed line being built along a highway](/wiki/File:NIM_Baustelle2001_Leidorf_Koeschinger_Forst.jpg "NIM Baustelle2001 Leidorf Koeschinger Forst.jpg")

The road\-rail parallel layout uses land beside highways for railway lines. Examples include Paris/Lyon and [Köln–Frankfurt](/wiki/K%C3%B6ln%E2%80%93Frankfurt_high-speed_rail_line "Köln–Frankfurt high-speed rail line") in which 15% and 70% of the track runs beside highways, respectively. There are [synergies](/wiki/Synergies "Synergies") to be achieved from such a setup as noise mitigation measures for the road benefit the railway and vice versa and furthermore less land must be taken through [expropriation](/wiki/Expropriation "Expropriation") as land may have already been acquired for the construction of the other infrastructure. In addition to that, habitats of local wildlife are disrupted only once (by the combined rail/road right of way) instead of at multiple points. However, downsides include the fact that roads usually allow steeper grades and sharper turns than high\-speed rail lines and thus co\-locating them may not always be suitable. Moreover, both roads and railways often make use of narrow river valleys or mountain passes which do not allow a lot of infrastructure to be sited next to each other.


Can the road-rail parallel layout be used to reduce construction costs?