Bot­tle­necks around Ade­laide’s O-Bahn Busway are set to dis­si­pate with in­fra­struc­ture works de­signed to ease conges­tion forg­ing ahead fol­low­ing re­cent in­vest­ment

Bot­tle­necks around Ade­laide’s O-Bahn Busway are set to dis­si­pate with in­fra­struc­ture works de­signed to ease conges­tion forg­ing ahead, fol­low­ing a ma­jor in­vest­ment

ABC (Australia) - - CONTENTS - WORDS GREG KEANE

A unique el­e­ment of Ade­laide’s pub­lic trans­port mix is its O-Bahn busway net­work with kerb-guided steer­ing, al­low­ing op­er­a­tion in a tight work­ing en­ve­lope.

The ded­i­cated busway al­lows buses to op­er­ate with­out the dis­rup­tion and vari­abil­ity of travel on pub­lic roads.

The only prob­lem with this system is that when the buses exit the ded­i­cated net­work, they travel on con­gested pub­lic roads to reach and exit the CBD, cre­at­ing bot­tle­necks dur­ing peak hours.

In an ef­fort to ad­dress this, the South Aus­tralian Gov­ern­ment ini­ti­ated the $160 mil­lion O-Bahn City Ac­cess Project to ex­tend the O-Bahn ser­vice, re­duc­ing traf c conges­tion and de­lays – par­tic­u­larly on the In­ner Ring Route.

This ex­ten­sion, cur­rently be­ing con­structed by McCon­nell Dowell (MCD), is sched­uled for com­ple­tion late this year and will cre­ate around 450 jobs over the life of the project. Signicant el­e­ments of the project in­clude the pro­vi­sion of cen­tral in­bound and out­bound bus pri­or­ity lanes on Hack­ney Road be­tween Gil­ber­ton and the north­ern tun­nel por­tal.

This re­quires the cre­ation of a 650m tun­nel from Hack­ney Road/De­quet­teville Ter­race un­der Run­dle Park, Run­dle Street and Rymill Park, emerg­ing in Rymill Park to align with bus trafc on Gren­fell Street.

The ex­ist­ing bridge over the Tor­rens River on Hack­ney Road will be widened, and con­struc­tion of a sep­a­rate shared-use bridge over the Tor­rens River is un­der­way.

SMART IN­FRA­STRUC­TURE

The guid­ance fea­ture of the O-Bahn system ac­tu­ally re­duces the cost of a tun­nel com­pared to one that would be built to ac­com­mo­date con­ven­tional buses. Be­cause the buses travel along a track, the risk of col­lid­ing with the wall or an on­com­ing bus is elim­i­nated.

This means that a nar­rower tun­nel can be built, re­quir­ing only 800mm of sep­a­ra­tion be­tween the op­pos­ing car­riage­ways and 1000mm of clear­ance from the tun­nel walls. No widen­ing is re­quired for travel around a curve.

How­ever, the ra­dius of cur­va­ture needs to take into ac­count the line of sight for buses trav­el­ling in the same di­rec­tion to pro­vide adequate time for brak­ing to avoid a rearend col­li­sion.

Given the lo­ca­tion of the works in a long-es­tab­lished area close to the CBD, ser­vice lo­ca­tion and re­lo­ca­tion to pro­vide a clear path for tun­nel works to pro­ceed was a signicant chal­lenge. Ser­vices to be re­lo­cated and pro­tected in­clude wa­ter, sewer and gas mains; stormwa­ter sys­tems; and un­der­ground and over­head high­volt­age ca­bles.

The age of the area led to many unan­tic­i­pated is­sues such as old tram foot­ings be­neath the road and re­dun­dant stormwa­ter pits from a time when the road level was signicantly lower. While there were records of al­most all of the util­ity ser­vices still in use, in­clud­ing sewer and wa­ter pipes that were more than 130 years old, the lo­ca­tion of many of the ser­vices had to be re-sur­veyed.

A par­tic­u­lar chal­lenge was the ex­is­tence of 66kV ca­bles in Run­dle Park. Th­ese ca­bles were tem­po­rar­ily de-en­er­gised and a sec­tion of the tun­nel was con­structed while the ca­bles were sus­pended above the ex­ca­va­tion on a tem­po­rary bridge.

TUN­NEL METH­ODS

The bus tun­nel is be­ing com­pleted us­ing a mix of cut and cover in the parks and top-down con­struc­tion in the road align­ment.

The cut-and-cover method is ideal as it min­imises the work area and the dis­rup­tion to trafc. Road pos­ses­sion is re­quired to in­stall sheet piles for the side walls of the tun­nel and roof beams over the top of the sheet piles.

Once the road is re­in­stated, ex­ca­va­tion can take place be­tween

the sheet piles be­neath live trafc, and the tun­nel oor and per­ma­nent walls can then be in­stalled.

The sheet pil­ing, roof beam in­stal­la­tion and road re­in­state­ment works for the Hack­ney Road/ Botanic Road in­ter­sec­tion works took place as a se­ries of night works in Septem­ber-Oc­to­ber. Cut-and­cover works in Run­dle Park and Rymill Park reached the 60 per cent com­ple­tion mile­stone in Novem­ber 2016 and are sched­uled for struc­tural com­ple­tion in mid-2017.

The tun­nel is pre­dom­i­nantly a re­in­forced con­crete struc­ture, with the oor slab and most of the walls poured in situ. Other than where the tun­nel crosses un­der the 66kV ca­bles, the tun­nel roof com­prises pre-stressed con­crete planks cast in Pooraka and trans­ported to site.

Ground­wa­ter has been en­coun­tered within Rymill Park, De­quet­teville Ter­race and Hack­ney Road, but once con­struc­tion is com­pleted, the tun­nel will be sealed to pre­vent ground­wa­ter ingress.

TRAF­FIC MAN­AGE­MENT

Be­cause of heavy ex­ist­ing trafc lev­els, trafc man­age­ment is a crit­i­cal is­sue on this project to minimise dis­rup­tion and al­low safe en­try and exit of con­struc­tion ve­hi­cles, as well as pro­vide a safe en­vi­ron­ment for work­ers.

A key step was to ban all right turns (ex­cept for buses and emer­gency ve­hi­cles turn­ing right from Hack­ney Road to Botanic Road) at the in­ter­sec­tion of Hack­ney Road, Botanic Road, De­quet­teville Ter­race and North Ter­race.

This was heav­ily pub­li­cised in the me­dia and through other chan­nels prior to im­ple­men­ta­tion. Conges­tion was suc­cess­fully re­duced by this mea­sure.

Th­ese bans will re­main in place un­til mid-2017.

Right turns have also been banned at other lo­ca­tions along Hack­ney Road, and some of th­ese will re­main in place, with U-turn fa­cil­i­ties im­ple­mented to cover their loss.

A min­i­mum of two lanes in each di­rec­tion is be­ing main­tained along Hack­ney Road, De­quet­teville Ter­race, North Ter­race and Botanic Road dur­ing peak pe­ri­ods (7am-10am and 3pm-7pm), and two in­bound lanes and one out­bound lane are be­ing main­tained along Run­dle Road through­out con­struc­tion of the tun­nel.

A Trafc Li­ai­son Group meets reg­u­larly to dis­cuss and rene trafc plans. Mem­bers in­clude the Department of Plan­ning, Trans­port and In­fra­struc­ture (DPTI) bus op­er­a­tions, Trafc Man­age­ment Cen­tre (TMC), Tor­rens Tran­sit, Ade­laide City Coun­cil, Town of Walk­erville, Nor­wood, Payne­ham and St Peters Coun­cil, Taxi Coun­cil, South Aus­tralian Road Trans­port As­so­ci­a­tion (SARTA) and emer­gency ser­vices.

PROGRESS TO DATE

To date, East Ter­race has been re­aligned and is open to traf c, park­ing has been re­moved from the west­ern side of Hack­ney Road, cen­tral pri­or­ity bus lanes are in op­er­a­tion on Hack­ney Road be­tween Gil­ber­ton and the Botanic Road in­ter­sec­tion (other than the out­bound lane be­tween the bridge over the Tor­rens River and the Gil­ber­ton por­tal), and a new south­ern park­ing area has been opened.

The beams for the pedes­trian bridge over the Tor­rens River were placed in July 2016, with work on the ex­posed ag­gre­gate deck and balustrad­ing com­pleted late last year. The new shared-use path along­side the Botanic Gar­den is sched­uled for open­ing in mid-2017.

Work on the civil as­pects of the tun­nel will con­tinue through to mid-2017, and will be fol­lowed by tout, test­ing and com­mis­sion­ing for an open­ing in late this year.

Widen­ing of the Hack­ney Road Bridge over the Tor­rens River will con­tinue into early 2017. Its com­ple­tion will al­low the out­bound bus pri­or­ity lane to be com­pleted

The guid­ance fea­ture ac­tu­ally re­duces the cost

through to the Gil­ber­ton por­tal of the ex­ist­ing O-Bahn.

Work on re­in­state­ment of park lands is tak­ing place pro­gres­sively as the tun­nel is com­pleted and back  lled. This in­cludes the in­te­gra­tion of a par­cel of land freed up by the re­align­ment of East Ter­race, and the re­lo­ca­tion of a foun­tain lo­cated in this precinct.

Works are un­der­taken as re­quired to en­sure that adequate ac­cess is main­tained for ma­jor pub­lic events tak­ing place in and around the park lands where con­struc­tion is tak­ing place.

Main pic­ture: Ade­laide’s O-Bahn has a unique de­sign

Left: Bus tran­sit is key in South Aus­tralia’s cap­tial city

Above: You can’t get a bet­ter bus pri­or­ity lane than this

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