The literature on access prices and investment has suggested that firms under-invest when subject to an access provision obligation combined with a fixed access price per consumer. In this paper, I study an access price per consumer for an innovative service such as superfast broadband provided by a regulated firm that is a function of its geographical coverage (indexation approach). The indexation approach can enhance economic efficiency beyond what is achieved with a fixed access price under a set of standard assumptions. In particular, it can simultaneously induce the firms to set lower retail prices, lead to wider geographical coverage of innovative services and higher social welfare level compared with a fixed access price. Moreover, in the model, the indexation may be used to achieve approximately the Ramsey outcome, or the first-best coverage level. I address how a regulator can set the access price indexation optimally, based on the coverage cost plus an incentive. I highlight the potential role of indexation as a tool to reduce the need for public subsidies and the associated tax distortions when compared with a fixed access price.