Analysing Utility Tunnels and Highway Networks Coordination Dilemma

Tunnelling and Underground Space Technology 24 (2009) 185–189

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Tunnelling and Underground Space Technology

journal homepage: www.elsevier .com/locate / tust

Analysing utility tunnels and highway networks coordination dilemma

Julian Canto-Perello a,*, Jorge Curiel-Esparza b, Vicente Calvo c

a Departamento de Ingenieria de la Construccion y Proyectos de Ingenieria Civil, Universidad Politecnica de Valencia, Camino de Vera, s/n 46022 Valencia, Spainb Escuela Tecnica Superior de Ingenieros de Caminos, Canales y Puertos, Universidad Politecnica de Valencia, Camino de Vera, s/n, 46022 Valencia, Spainc Escuela Tecnica Superior de Ingenieros de Telecomunicaciones, Universidad Politecnica de Valencia, Camino de Vera, s/n, 46022 Valencia, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 June 2008Received in revised form 28 July 2008Accepted 29 July 2008Available online 23 September 2008

Keywords:Utility tunnelUtilidorsTransportation networksUnderground sustainabilityUrban planning

0886-7798/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.tust.2008.07.004

* Corresponding author. Tel.: +34 963877000; fax:E-mail addresses: [email protected] (J. Canto-P

Curiel-Esparza), [email protected] (V. Calvo).

Utilities are an integral component of the total transportation network comprising highways, railways,airways, and waterways, as well as pipelines, wires, and cables that transport people, goods, and publicservices. The perennial dilemma of mutual interference between utility lines and transportation net-works could be minimised making use of utility tunnel systems. Utilidors most striking feature is thatthey house several types of power, water, sewage, communications, gas and other statutory services inan easily accessible space. Placing utilities in tunnels under public rights-of-way reduces the continualcutting of pavements resulting from utility burial practices and facilitates the installation, inspection,replacement, and maintenance operations. Utility tunnels and transportation networks may not be com-patible at transmission levels. Highway systems are generally planned to avoid high-density areas insofaras is possible. However, where the location of utility networks coincides sufficiently with the highwayroutes, the situation becomes more favourable to the utility tunnel concept. This paper discusses howcompatibility of utility system networks with highway system networks could be greatly improved byappropriate attention to utilidor systems in urban planning. A sustainable approach to the dilemma ofwhere to locate utilities in urban streets and highways has become urgent as the need for servicesexpands in our modern cities. Interference between the safety and flow of highway traffic and utility tun-nel operation could be a problem unless adequate measures are undertaken.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Efficient and reliable highway and utility systems are key fac-tors to live in a modern society (Carmody and Sterling, 1993; Duf-faut, 1996; Duffaut and Labbe, 2002). The construction of anyunderground infrastructure involves a consumption of subsurfacespace. Moreover, these facilities will take up the subsurface evenwhen they become outdated. The growing scarcity of available realestate and its rising cost are forcing the consideration and use oftechnical designs involving joint utilization of right-of-way to re-duce utility space consumption (Cano-Hurtado and Canto-Perello,1999). The shallow urban underground is a non-renewable re-source. Therefore, these facilities must include environmental sus-tainability parameters in their design. Sustainability is defined as‘‘meeting the needs of the present generation without compromis-ing the ability of future generations to meet their needs”, accordingto the Brundtland Report of the UN’s World Commission on Envi-ronment and Development (Brundtland, 1987). For municipal engi-neers involved in design and construction of utilities, sustainablestrategies must be a tool to use resources adequately; minimising

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+34 963879569.erello), [email protected] (J.

damage to the environment and ensuring future subsurface useswill not be affected (ITA, 2004). Therefore, there is an increasinginterest in utility tunnels as a problem-solving technique to avoidcongestion of the rights-of-way. A multi-utility tunnel is defined asan underground facility containing one or more utility systems,permitting the installation, maintenance and removal of the utili-ties without making street cuts or excavations (see Fig. 1). How-ever, managing these underground facilities is always challengingdue to synergistic issues.

Establishing future sustainable strategies in urban undergroundengineering consists of the ability to lessen the use of traditionaltrenching (Curiel-Esparza et al., 2004). Obviously, this task goes be-yond the role of a short-term urban planning. Use of utility tunnelsprovides necessary space for statutory services, involving under-ground pipes and cables, with minimum environmental impact(Canto-Perello and Curiel-Esparza, 2001). Moreover, utilidors guar-antee the underground space resources for future generations. Inconsidering the viability of utilidors in coordination with high-ways, it is necessary to compare conventional utility and transpor-tation systems layouts and characteristics. The purpose of thispaper is to analyse the advantages and disadvantages of utilidorpractice in highway networks. However, the potential compatibil-ity problems may also include interference of utilities amongthemselves operating in a tunnel environment.

Fig. 1. Utility tunnels promote joint use of underground rights-of-way highway.These facilities may contain water, sewerage, electrical power, gas, telephone andcentral heating.

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2. Utility tunnel historic review

Generally, few cities appear to have considered the systematicbuilding of utilidors in existing highways or streets for the reasonthat the expense is considered prohibitive. The history of modernutility tunnels dates back to the nineteenth century. Water pipesand electric cables were added to the sewer of Paris and a Londonsystem commenced. In the great scheme of the municipalimprovement of Paris, which was started under the direction ofBaron Haussman about 1851, a comprehensive system of subwayswas included; the main sewer was designed to form both sewersand utility tunnels (Engineering News, 1907). The London subwaysdate from 1861, when a new street was opened from Covent Gar-den Market to St. Martin’s Lane, having a central arched passage-way beneath it, 3.66 m wide and 1.98 m high, with branches forthe various house connections from the water, gas and telegraphmains (Engineering News, 1900). The system has since been ex-tended as fast and as far as opportunity offered, and is of such con-spicuous public benefit that the County Council was committed tothe policy of making it part of every scheme of street improvementundertaken its direction. Some regard it as a crime against the pub-lic interest that pipe galleries were not built in connection withevery foot Rapid Transit Subway thus far constructed (Baylis,1904). Nowadays, utility tunnel construction projects have in-creased at cities where olympic games or any other mega eventhave been celebrated during the last decades. Cities like Tokyo(1964), Barcelona (1992) (see Fig. 2), and Athens (2004) have reac-tivated utility tunnel projects along the major routes of services tofacilitate installation and maintenance of utilities throughout thesite (Hadjihambi and Deriziotis, 2002; Malfas et al., 2004).

In the United States, the ‘‘Program Guide Utility Relocation andAccommodation on Federal-Aid Highway Projects”, prepared bythe Federal Highway Administration, has considered the use ofutility tunnels to locate their facilities on highway rights-of-way,when such use and occupancy does not adversely impact highwayor traffic safety, or otherwise impair the highway or its aestheticquality, and does not conflict with State or local laws or regula-tions. Underground space is finite and authorities should includeutility tunnels in highway projects, and use their own funds topay them in order to better manage utility use and occupancy oftheir highway rights-of-way (FHWA, 2003). The increasing de-mands for underground solutions emphasise the need for bettercoordination of the utilization of underground space (ITA, 2000).In addition, an important obstacle for many utility tunnel projectsis the number of different authorities, federal departments andoverlapping legislative documents that must be approved beforethe road works begin.

3. Advantages and disadvantages of utility tunnel practice

Utilities have traditionally been permitted to use highwayrights-of-way for location in either aboveground or undergroundmode. However, location of utilities in the underground case gen-erally has not been accomplished in any systematic manner. Thetraditional practice of burying each utility in separate trenchesacross the road rights-of-way will be compared with the use ofutilidor to illustrate the pros and cons of both systems. It is knownthat directly buried systems do not require ducts or linings andutility installation is cheaper and faster than for a utilidor system(Canto-Perello and Curiel-Esparza, 2006). In addition, the amountof excavation required per utility is minimal, because space isneeded only for a cable or a pipe. However, the total future cost in-curred due to the excavation of highways for expansion, mainte-nance and replacement of utilities has never been thoroughlyevaluated when this directly buried system is used. Experienceshows that the use of utility tunnels increases reliability and de-creases maintenance cost, increasing their effective life. Moreover,utilidors can be inspected periodically to identify safety hazards,and these operations can be done under all climatic conditions.The principal failure hazard of utility structure arises from the lackof routine inspections (Madryas, 2008). The use of utility tunnelsimproves safety and security for some or all utility occupants be-cause they are designed to minimise personal injuries and preventaccidents (Canto-Perello and Curiel-Esparza, 2003). However, thecompatibility between conduits of different services must be ana-lysed to avoid interference, and the possibility of damage on oneutility while working on another should be taken into account.

Future installation and expansion of utility systems can be per-formed without excavation when utilidor system is used, eliminat-ing traffic interruption, reducing highway maintenance costs, andlengthening pavement life (the life of a pavement is in inverse pro-portion to the number of openings made in it). If a trenching sys-tem is adopted, every utility addition or expansion involves newexcavation and increases the likelihood of damage to other utili-ties. In addition, two-thirds of street openings are made to installor repair water, gas mains and services. A change in methods oftraditional burial for utilities never comes easily. Utilidors areone of the most sustainable underground facilities and must there-fore be included in highway planning.

Utility tunnels show some requirements that imply an increaseof the total investment. A ventilation system to ensure adequate airsupply for workers, interior illumination, emergency systems,drainage facilities to handle seepage or flooding, and periodic ver-tical access and emergency exits should be included in the initialdesign (Curiel-Esparza and Canto-Perello, 2005). In addition, utilitytunnels finely tuned to current demands in space requirements

Fig. 2. Barcelona’s utility tunnel plan was proposed in 1989 by the local authority to profit the right-of-way of a new ring highway system. The main objective of theseinfrastructures was to connect the four major olympic areas. The involved area was a strip of 1 km wide, on a ring highway of 25 km long where utilidors lie parallel to thering highway.

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will soon become outdated. Summarizing, the primary advantagesof utilidor systems are the reduction or elimination of highwaycuts, eliminating interferences with traffic, reducing street noiseand damages to other utilities; increase or expansion of utilitieswithout disruption of traffic; and the reduction of utility rights-of-way requirements. The main disadvantages are the increasedcost and complexity in characterizing the existing space, coordi-nating installation and ensuring compatibility for maintenanceactivities. However, advantages of utility tunnels indubitably out-weigh the disadvantages in many situations.

4. Compatibility between utility tunnels and highway networks

Utilities form part of the total transportation network, which iscomprised of highways, railways, waterways, etc. There is a basiccharacteristic between them; transportation and utility networksshare the common feature of being population oriented. In an ide-alized situation it may be expected that the transmission objec-tives of these networks would coincide to a certain extent.However, in considering the coordination of utilidors with high-ways, it is necessary to compare conventional utility and highwaynetwork layouts and characteristics. On rigorous economic justifi-cation, utility tunnels require high density of utilities to becomecost-effective. Moreover, full occupancy of an utilidor is more fea-sible for the distribution level than for the transmission level.

At the local street level in urban areas, the distribution functionof utility networks substantially coincides with the street layout,since essentially every abutting property must be served by everyutility. At the collector and arterial street level, the utility distribu-tion and transportation functions are not found to be consistentlypresent. At the highway level, the utility transmission functionsseem to be even less compatible with the higher traffic transporta-

tion networks than in the preceding cases. However, compatibilitymay be improved by more attention to potential utility tunnel sys-tems in the highway and utility network planning process.

The lack of compatibility to overcome may be attributed tomany factors. These include for example topography and geology.Sewage is topographically oriented because the grade requirementis usually preferred to the use of pumping facilities. Anyway, inclu-sion of storm sewers or combined storm and sanitary sewers inutilidors is impracticable due to the required big diameter of pipes(Abu Sier and Lansey, 2005). Furthermore, laying gravitationalsewage pipes in utility tunnels requires correlation of longitudinaldrops of both structures which can be difficult or even impossibleand hence these pipes are often left beyond utility tunnels. Otherfactors are the sources of utility supply, such as generating stationsor transmission switching stations, which are located usually inlow populated areas but not necessarily near highways. Real estateavailability and values dictate facility location usually. Moreover,telephone feeder lines are dependent on the location of telephonicexchanges, which are limited in geographical range and must belocated nearby to centres of population. Fragmentation of utilityservice entities and lack of coordination with highway authoritieswill enlarge these circumstances. In addition, city highways areplanned to avoid high-populated areas insofar as is practicable.Therefore, only the utility transmission function is likely feasible.Furthermore, highways have been in many cases constructed aftermajor utility layouts were established.

5. Highways and utility tunnels location

Due to the number of necessary utilities, utility tunnels presentmore attractiveness in the central business and commercial dis-tricts. Existing utility tunnels are mostly located in arterial and col-

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lector streets of these areas, which provide conventional free ac-cess to abutting property owners in high-density blocks, and aretypically highly congested with traffic. Where the arterials and col-lector streets have medians or frontage streets with separationstrips, utilidors may be placed under the medians or separationstrips, or under street edges or sidewalks. Utility tunnels underthe median need generally lateral access tunnels from near therights-of-way lines to reduce conflicts with traffic flow by servicemaintenance operations. This location of utility tunnels would re-quire long service lines to abutting property owners, thereforeminimising the potential benefits of the utilidors. Favourable lay-out positioning for utility tunnels would be under sidewalks, streetedges, or frontage street separation strips. In comparison with arte-rial and collector streets, utility and highway networks are not gen-erally as much compatible and will be discussed in the followingparagraphs.

In rural areas, highways usually avoid populated areas. There-fore, service needs for abutting properties are of low density andutility tunnels are economically unfeasible. Where highways passthrough urban areas, the situation improves for utilidors. The po-tential sizes and number of utilities collected by an utilidor in thesesituations will depend on the population density and the nature ofthe utility networks. In urban areas, medians tend to be narrow.Entranceways may cause highway safety issues.

Interference with the flow of traffic will be unavoidable unlessadequate measures can be planned for employees and service vehi-cles to gain access to the utilidor from other than the through traf-fic lanes, such as lateral access by a tunnel (see Fig. 3).

Fig. 3. Barcelona’s utility tunnel entrance located near a highway right-of-way.Utility tunnel security is another matter of great concern. Limiting the number ofentrances and exits for personnel and material, plus strict sign-in and sign-outprocedures offer the greatest security in existing utility tunnels.

Additional costs will be necessary if these accesses do not coin-cide with those used to serve abutting properties. Obviously, utilitytunnels could be constructed on both sides near the rights-of-wayline. Connecting tunnels should be used to provide layout flexibil-ity between the two tunnels at intervals. However, a large numberof utility lines would be required to justify the extra expense ofconstruction.

In high-density urban areas, highways can be constructed indepressions in order to keep street crossings on original grades,and to minimise aesthetic impact or traffic noise. These situationsalso present opportunities for utility tunnels; the retaining wallsupporting the excavation can form the outside of the utilidor.Entranceways can be accessible from the frontage street presentin most cases. Elevated highways may present access problemsto incorporate utility tunnels. Moreover, interference with pedestalfoundations disqualifies the subsurface right-of-way upon whichthe elevated facility is placed. The key designing factor for mosthighway situations will be safety access without interference withtraffic flow. Feasibility of utilidors depends largely in overcomingthe costs of this requirement.

6. Conclusion

Historically, utilities have always had a license or a franchise tooccupy the streets and highways, subject to the lawful exercise ofthe police powers of the state. There is a growing trend for jointdevelopment and multiple use of the space below and above thehighway right-of-way. The feasibility of constructing utility tun-nels in conjunction with transportation facilities will depend inpart on the compatibility of utility system networks with transpor-tation networks. From the broad point of view, transportation andutility systems share the common characteristic of being popula-tion oriented. Both infrastructures can be defined as classical net-works whose location on the ground is primarily governed bypopulation distribution in terms of extent, average density, andconcentration. In an idealized situation it might be expected thatthe transmission function of the various utilities would coincidewith the highway system; the utilities primary distribution func-tion with arterial and collector streets; and the secondary distribu-tion function with the local street networks. Many factors tend toupset this idealized concept in existing urban areas.

A sustainable strategy to the dilemma of how and where toplace utilities in urban streets and highways has become urgentas the need for statutory services increases. The question of util-ity location in heavily travelled highways where installation andmaintenance affect the vehicular traffic must be a key factor inurban planning. Moreover, the structural damage to the roadpaving and foundation by utility cuts is a matter of great con-cern. In response to these problems, utility tunnels became sig-nificant not only for preventing the need to dig up the roadsfor repair, but also for the efficient use of the valuable space un-der the highway. Rights-of-way space is a finite and non-renew-able resource. For municipal engineers involved in design andconstruction of utilities, sustainable strategies must be a tool ofdoing things that uses resources adequately, minimising damageto the environment and ensuring future subsurface uses will notbe affected.

Usually, urban policies are not established unless there are con-vincing needs to do so. The habitual procedure is to meet problemsas they arise in current practice. Now, while disputes about use ofrights-of-way for utilities are under control, is the turning point tohandle future demands. Utility system networks and highwaytransportation networks are not generally compatible at the levelof utility system transmission and highway. They become morenearly compatible at the utility system primary distribution andcollector street level, and they are fully compatible at the utility

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system secondary distribution system and local street level, whereessentially every street contains every utility. Therefore, the suc-cess of any highway project incorporating utility tunnels will de-pend upon the cooperation and agreement of all authoritiesconcerned. The policies and practices of local authorities, publicand private companies and the various regulatory bodies must bean encouraging factor for the development of utility tunnel sys-tems through all phases of planning, financing, construction andoperation. A change in methods of traditional burial never comeseasily, although it will inevitably be necessary.

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