The M50 is facing “failure” if tolling is not introduced on the entire length of the motorway Transport Infrastructure Ireland (TII) has told an Oireachtas transport committee.

The State transport body wants to introduce “multipoint” electronic tolling along the M50 on a junction-by-junction basis instead of having a single toll point that only one quarter of the road’s users pass through.

Successive transport ministers, including the current Taoiseach Leo Varadkar and Minister for Finance Pachal Donohoe, have ruled out multipoint tolling because of a lack of public transport capacity and the risk of increasing traffic congestion on surrounding residential roads.

TII chief executive Michael Nolan said the M50 was approaching the point of “intolerable congestion” which would make it unusable at peak times.

He said lower rush hour speed limits are due to be implemented on the road from the end of next year or the start of 2020, once legislation has been introduced, in a bid to improve traffic flow.

Variable speed limits would also reduce minor “read end” collisions, he said.

“Unfortunately, an incident in one direction causes almost equivalent delays in the opposite direction due to ‘rubber-necking’.

However, he said this would not be sufficient to fix congestion and “we are at a point that can’t keep building out on the M50.”

Without multipoint tolling, “the level of traffic growth will ultimately result in an intolerable level of congestion and economic loss and the failure of the motorway to adequately fulfil its strategic functions”, Mr Nolan said.

This did need to be complemented by continuing public transport investment, he said. Five of the seven new longer Luas trams which were withdrawn earlier this year due to an electrical fault were now in service, Mr Nolan said. The sixth tram is due to enter passenger service in the next week, and the seventh tram is due to be delivered on May 25th.

These longer trams “have greatly improved the tram availability situation” he said. By 2021, 26 existing short trams would be lengthened and eight new long trams would be bought he said.

The redesigned Dublin bus network, with reconfigured routes, schedules and fare structures, would be published in July as part of the Bus Connects programme, deputy chief executive of Transport Infrastructure Ireland Hugh Creegan told the committee.

Plans for investment in infrastructure on the 16 core bus corridors in and out of the city, would be published in October he said.

A 10 minute Dart service would be provide later this year following the resolution of driver training issues, he added.

Before the M50 was widened in 2010 it had been a “mathematical certainty the M50 was going to gridlock” Green Party TD Eamon Ryan said. While it was clear public transport needed investment ahead of road improvements “all the investment has gone in the opposite direction” he said.

Fianna Fáil TD John Lahart said multipoint tolling would have “catastrophic consequences” for residential areas.

“You need to forget multipoint tolling,” he said “Just drop it and stop bringing it up.”

Mr Nolan said it was a “matter for Government”.