The North West Rail Link (NWRL) is to be a new railway line from Chatswood to Rouse Hill. It's a very desirable project which will extend rapid reliable public transport into a large new sector. The plan is to introduce single-deck trains onto it. The Minister wants to make this railway the first Tier 1 line in an expanded CityRail network.

Roughly, Tier 1 trains are to be single-deck metro cars like those in many other cities. Tier 2 trains will be double-deck services covering most of the present suburban network. Tier 3 trains will be longer-distance trains including former Countrylink services.

The government determined that the NWRL should be a Tier 1 Railway. We believe this is the wrong decision.

The plan was forced through without relevant public consultation, apparently in an attempt to conceal its disadvantages. We have a government that thinks in projects, not in how to grow the transport network to keep up with the needs of a rapidly-expanding city.

The immediate problem is that the tunnels from Epping to Bella Vista are to be bored slightly too narrow (and with some slopes slightly too steep) for current double-deck trains. This means the NWRL trains will have to be single deck. Single deck trains have fewer seats than double deck trains, meaning more passengers will be required to stand.

Unsurprisingly, constraints which permanently prevent using those tunnels for double-deck trains will have an adverse effect on developing the rail network. Several experts have investigated the matter and reported in great detail - see references at foot.

As the saying goes, it's a matter of "horses for courses". Double-deck trains are preferable for longer trips, because passengers don't like standing for long. Single-deck trains with minimal seating and lots of doors work well for short trips with closely-spaced stations, typically about 1km apart.

Our double-deck trains handle an average trip length of about 20km. The NWRL is catering for journeys that average well over 20 kilometres and would take much more than 20 minutes. There is a long-standing CityRail policy that no-one should have to stand for longer than 20 minutes, which APTNSW agrees is reasonable. On these longer journeys, trains should have more passengers seated and fewer standing, precisely what double-deck trains have.

Also, by making these tunnels double deck, we would allow trains from the city to go all the way to Rouse Hill, without the need to change at Chatswood. Cities such as Paris use double deck trains on lines whose passengers travel on longer journeys and single deck trains for shorter journeys on its Metro.

No. Single-deck trains would work well for shorter trips in the inner suburbs. Most of the inner suburban stations in Sydney are spaced at about 1.5km. However as stated above, the NWRL is an outer suburban line for people making long journeys. NWRL stations average 3km apart, including a 6km gap between Epping and Cherrybrook, and thus require services with a full complement of seats.

If Sydney is to get a new type of train, we should ensure it's the best choice for our system and its location.

• The tunnels and stations from Epping lower level to Chatswood platforms 2 and 3 will have to be converted (the official pronouncements say "upgraded") to handle the new trains. This is expected to take seven months, and that after four months of shuttle running. For however many months the conversion takes, all passengers at Macquarie University, Macquarie Park and North Ryde stations will have to ride substitute buses. At least 14000 people will be affected, typically twice per day. Where will the extra bus stops be? - there's no spare space at existing stops.

• Many people who currently have unbroken train trips will have to change trains once or twice per trip. This disadvantage will continue so long as a totally new CBD railway, with new Harbour crossing, is not built. Even casual observers can see that recent NSW governments have been less than keen to make such huge investments in public transport.

• The M2 buses will become feeders to the nearest NWRL station. While the Wynyard area will benefit from less congestion, most bus-train trips will take longer than bus alone currently takes.

• The new railway will be operated as a public-private partnership. Insolvencies with the Airport railway, the Lane Cove road tunnel and the cross-city tunnel are well-known in the finance industry. The NWRL operators will presumably insist on profits flowing to them and risks being carried by the State.

Unless and until a new railway from about Redfern to Chatswood is built, the NWRL cannot work properly. Studies have identified that more than two-thirds of NWRL users will have to continue their journey beyond Chatswood. This means incredibly large crowds of people changing to board already-crowded North Shore Line trains.

Some commentators point out that the overcrowding will put irresistible pressure on the NSW government to build a new harbour crossing and CBD line sooner rather than later. That's plausible but NSW Treasury can be expected to delay and delay such an expensive suggestion. It is noteworthy that recent Government publications state the eventual crossing will be a submarine tunnel when cheaper options using the Harbour Bridge would seem to be available.

Double-deck trains served Olympic Park station well in 2000, carrying over 25000 passengers per hour. It's not just how many decks or doors the trains have, it's also station design, signalling, etc.

And a 6-car single-deck train with a claimed capacity of 975 passengers will have only about 375 seats. The other 600 passengers will be standing, at four to the square metre. Think of standing on a square 50cm x 50cm! Expert advice (see references below) is that double-deck trains provide more seats per track per hour than single-deck.

There are plenty of ways to skin a cat. Improved signalling as well as rolling stock with more doors could increase the number of double deck trains per hour on a train line. Overall, these measures could deliver more seats and more spaces overall than a single deck system.

It might have been possible to commission the line in stages from Epping, possibly allowing earlier opening.

There might have been no need for a separate depot; fewer trains would have been required because of reduced changes.

Modernising NSW railways would of course be desirable but it won't happen overnight. Driverless trains might be okay on a fully-enclosed system of tunnels and viaducts like the NWRL but the prevalence of graffiti around CityRail tracks shows how difficult it can be to keep intruders out of a large network.

It has not yet been announced whether the NWRL trains are to have any crew at all, such as an attendant who could help passengers if required.

It was more a political decision than a logical one. Sydney's entire CityRail network was single deck until the 1960s when it was converted in order to increase seating capacity. This conversion happened gradually, without great inconvenience. As the North West growth corridor expands, demand may dictate the need for double deck trains. The NWRL should be built as double deck now to avoid the inconvenience and increased cost in the future, as well as to deliver greater capacity.

There was, but the NWRL plan came out during preparation of the master plan. Cynics might say that was to prevent the master plan getting the wrong answer.

There's a full list of references here. A good start would be the paper "1855 Revisited" by Sandy Thomas (landscape or portrait).

A careful discussion by Alex Wardrop of the relative merits for Sydney of double- and single-deck trains can be found in Appendix 3 of this report

You could send a message direct to the Minister for Transport here.

You could email your local state MP. For example, if you live in the state electorate of Tritown, the address of your local member is tritown@parliament.nsw.gov.au

Tell them it's imperative that the NWRL tunnels be re-designed to be capable of carrying existing double-deck trains. You could also say that full compatibility of the new trains with existing tracks would lessen the pain of conversion.

You could also join APTNSW.