Proposals for expansion of the Melbourne rail network are commonly presented by political parties, government agencies, industry organisations and public transport advocacy groups. The extensions proposed take a variety of forms: electrification of existing routes to incorporate them into the suburban rail system; reconstruction of former passenger rail lines along pre-existing easements; entirely new routes intended to serve new areas with heavy rail or provide alternative routes in congested areas; or track amplification along existing routes to provide segregation of services. Other proposals are for the construction of new or relocated stations on existing lines, to provide improved access to public transport services.