Restrictions on car access to the park will also apply.
A new 30 kilometre an hour speed limit comes into force in the Phoenix Park in Dublin from today.
There will also be restrictions on car access to the park, as announced earlier this month.
The new limits and restrictions are in line with the recommendations of the Phoenix Park Transport and Mobility Operations Report, which was published in January last year.
In addition to the new speed limits, the Office of Public Works has also implemented a one-way system on the North Road, while cars will be banned altogether from using the park's main southern Road.
Meanwhile, temporary cycle lanes which replaced parking on Chesterfield Avenue will become permanent.
According to the Irish Times, a high visibility Garda presence will be in force to patrol the new measures, which has been described as one of the most significant curbs on traffic in the park to date.
Additional measures could be introduced in the coming months, as the OPW says it is advancing its Parking Strategy, as contained in the report.
It says the strategy will aim to address parking issues and visitor requirements, especially those with mobility requirements.
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