RAIL passengers travelling between Eastleigh, Netley and Portsmouth will be on the buses this week.
Railtrack will be carrying out scheduled engineering work on the tracks until Sunday.
South West Trains says it will mean switching passengers to the road.
Train services between Eastleigh and Portsmouth will be replaced with buses for the complete journey, while trains between Southampton Central and Portsmouth will be replaced by buses between Netley and Portsmouth Harbour. Through train services are due to resume with the 1.47pm Portsmouth Harbour to Southampton and the 2.13pm Portsmouth Harbour to Eastleigh on Sunday.
The engineering works will also affect services operated by Wales and West. A South West Trains spokesman said: "Passengers travelling to or from stations on the affected routes should check the times of services with National Rail Inquiries on 08457 484950 before travelling."
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