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                            April 22, 2021

       John Erhard
       Chief Executive Officer
       ArcLight Clean Transition Corp.
       200 Clarendon Street, 55th Floor
       Boston, Massachusetts 02116

                                                        Re: ArcLight Clean
Transition Corp.
                                                            Amendment No. 1 to
                                                            Registration
Statement on Form S-4
                                                            Filed April 7, 2021
                                                            File No. 333-252674

       Dear Mr. Erhard:

             We have reviewed your amended registration statement and have the
following
       comments. In some of our comments, we may ask you to provide us with
information so we
       may better understand your disclosure.

              Please respond to this letter by amending your registration
statement and providing the
       requested information. If you do not believe our comments apply to your
facts and
       circumstances or do not believe an amendment is appropriate, please tell
us why in your
       response.

              After reviewing any amendment to your registration statement and
the information you
       provide in response to these comments, we may have additional comments.

       Amendment No. 1 to Form S-4

       Risk Factors, page 28

   1.                                                   We note your response
to comment 6. Please revise the introductory paragraph to clarify
                                                        that all material risks
have been disclosed.
       Risks Related To Proterra's Business Following the Business Combination
       Defects in the materials or workmanship of our composite bus bodies...,
page 29

   2.                                                   We note your revisions
in response to comment 5. Please disclose whether there has been
                                                        a material impact on
Proterra.
 John Erhard
FirstName   LastNameJohn
ArcLight Clean   Transition Erhard
                            Corp.
Comapany
April       NameArcLight Clean Transition Corp.
       22, 2021
April 222, 2021 Page 2
Page
FirstName LastName
Item 21. Exhibits and Financial Statement Schedules
5.1 Opinion of Kirkland & Ellis LLP, page II-1

3.       Please have counsel remove the assumptions in paragraph 6 of the legal
opinion. It is not
         appropriate for counsel to include in its opinion assumptions that
assume any of the
         material facts underlying the opinion. Refer to Section II.B.3.a of
Staff Legal Bulletin No.
         19.
       You may contact Effie Simpson at 202-551-3346 or Jean Yu at 202-551-3305
if you have
questions regarding comments on the financial statements and related matters.
Please contact
Erin Purnell at 202-551-3454 or Asia Timmons-Pierce at 202-551-3754 with any
other
questions.



                                                               Sincerely,

                                                               Division of
Corporation Finance
                                                               Office of
Manufacturing